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OB 46 IRVING ' S 

i72 ATECHISM 

Copy 1 0F 

^^ HsIotoj) ; 

CONTAINING THE 

MOTIONS, MAGNITUDES, PERIODS, DISTANCES, 

AND OTHER PHENOMENA 

OF THE 

HEAVENLY BODIES. 
<#ottnbto on % fafijs of fobiiafion. 

WITH ENGRAVED ILLUSTRATIONS. 
FIFTH AMEBICAX EDITION, REVISED AND IMPKOVED, 

By M. J. KERNE Y, A.M 

Author of Compendium of Ancient and Modem History, First Class 

of Z ?', T hism efm m ^ «~ v»™ 

Mates, Columbian Arithmetic, d-c. dc. dc. 



tf> «tapt«» to m ®m f s cIjoors in m mm Stet£s _ 
1r 

BALTIMORE.: 
PRINTED & PUBLISHED BY J. MURPHY & CO 

178 MARKET STREET. 
PITTSBURG. ..GEORGE QTJIGLEY 

Sold by Booksellers generally throughout the United States. 

1854. 



Entered according to the Act of Congress, in the year 1854, by 

JOHN MURPHY & CO. 

in the Clerk's Office of the District Court of Maryland. 



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PREFACE. 



The long established reputation of Irving's Cate- 
chisms precludes the necessity of adding any com- 
ments on their merits. The very extensive circula- 
tion which they have had, not only in England, but 
also in this country, is the best proof of their utility. 
The plan of his works is the very best that could be 
adopted. The catechetical form of instruction is 
now admitted, by the most experienced teachers, to 
be the best adapted to the nature and capacity of 
youth ; — a system by which children will acquire a 
knowledge of a science in less time than by any 
other. 

The present number on Astronomy will be found 
to possess peculiar merits. It is admirably adapted 
to that class of learners, for which it is designed. 
It presents, in a few words, to the mind of the pupil, 
the most important and most interesting points in 
the study of the science. 

The present edition has been carefully revised, 
and considerably improved. These improvements, 
it is believed, will add much to its merits, and render 
the work still more worthy of that liberal patronage, 
which has already been extended to it. 



CONTENTS. 



PAGE 

Preface 3 

Introduction. — Laws of Motion 7 

Apparent Motion of the Planets, direct, retro- 
grade, and stationary 8 

Gravitation 9 

Centripetal Force 4 . 9 

Centrifugal Force 9 

Chap. I. Astronomy 10 

II. History of Astronomy 11 

The Solar System 13 

III. The Sun 13 

IV. Eclipse of the Sun 16 

V. Mercury 17 

VI. Venus 19 

VII. The Earth 21 

VIII. The Moon 23 

IX. Eclipses of the Moon , 25 

Harvest Moon 27 

X. Mars....^ 27 

XL Vesta 28 

XII. Juno 30 

XIII. Ceres 31 

XIV. Pallas .: 32 

XV. Origin of Ceres, Pallas, Juno, and Vesta 33 

XVI. Jupiter 35 

XVII. Jupiter's Satellites 37 

XVIII. Saturn 39 

XIX. Satellites of Saturn 41 

XX. Herschel, or the Georgium Sidus 42 

XXL Satellites of Herschel 43 

XXII. Comets 45 

XXIII. Fixed Stars 46 

XXIV. Constellations 48 

1* 5 



CONTENTS. ^ 

XXV. North of the Zodiac 49 

XXVI. In the Zodiac 51 

South of the Zodiac 52 

XXVII. Aurora Borealis 54 

Zodiacal Lights 55 

The Galaxy, or Milky Way 55 

XXVIII. The Tides 56 

XXIX. Theory of the Tides 57 

XXX. Atmosphere; Wind; Rain, <fec 58 

XXXI. Of Globes 61 

Problems performed by the Terrestrial Globe 62 

Problems on the Celestial Globe 70 

Appendix, containing Astronomical Terms 74 



ffiafejfam «t ^ijma%. 



INTRODUCTION. 



Laws of Motion, Gravitation, Centripetal Force, 
and Centrifugal Force. 

MOTION. 

Q. What is Motion ? 

A. Motion is a continued and successive change of 
place. 

Q. What is the general tendency of bodies ? 

A. A body is indifferent as to motion or rest ; but, 
when once put in motion, it would continue to move, 
were it not interrupted by some external cause. 

Q. How many kinds of motion are there ? 

A. Motion, in astronomy, may be divided into sim- 
ple and compound, real and apparent. 

Q. What is simple motion ? 

A. Simple motion is that motion which is produced 
by one force acting upon and impelling a body. 

Q. In what direction is simple motion ? 

7 



8 INTRODUCTION. 

A. A body impelled by one force, will move in a 
straight line. 

Q. What is compound motion ? 

A. Compound motion is produced by two or more 
forces, acting upon a body. 

Q. In what direction does the body move ? 

A. When a body is impelled by two forces, acting 
in different directions, it obeys neither, but moves 
in a line between them. 

Q. What is real motion ? 

A. Real motion, in astronomy, is a successive change 
of place ; as, the earth's annual and diurnal mo- 
tions. 

Q. What is apparent motion ? 

A, Apparent motion is an apparent change of place, 
when the body or object is actually at rest. 

Q. Can you give an example of this motion ? 

A. Yes ; in sailing along the shore of a lake, bay, 
&c, we observe that the trees, houses, and other 
objects seem to move in a contrary direction to that 
of the vessel ; but this motion is only apparent, and 
produced by the real motion of the vessel. 

APPARENT MOTIONS OF THE PLANETS, DIRECT, RETRO- 
GRADE, AND STATIONARY. 

Q. What is meant by the direct motion of a planet? 

A. The motion of a planet is said to be direct, 
when it is farthest from us ; as d, Plate II. Fig. k. 

Q. What is the retrograde motion of a planet ? 

A. The planets are said to move retrograde when 
nearest to us, at which time they seem to move back- 
wards ; as r, Plate II. Fig. k. 

Q. When is a planet said to be stationary ? 

A. The planets, though actually in motion, are said 
to be stationary, when they are near to us, either in 
approaching or going from us, as s, Plate II. Fig, k. 



INTRODUCTION. 9 

Q. What is the cause of these appearances ? 

A. The planets appear direct, stationary and retro- 
grade, because they do not move round the earth as 
a centre. 

GRAVITATION. 

Q. What is Gravitation ? 

A. Gravitation, in astronomy, is that principal or 
law by which the planets tend toward the Sun, and 
the Sun toward them. 

CENTRIPETAL FORCE. 

Q. What is Centripetal Force ? 

A. Centripetal, or attractive force, is that by which 
a moving body tends, or is drawn immediately to- 
ward a centre, and made to revolve in a curve. 

CENTRIFUGAL FORCE. 

Q. What is Centrifugal Force ? 

A. Centrifugal or projectile force, is that by which 
a body revolving about a centre, or about another 
body, endeavors to fly off from it. 

Q. How are these forces regulated ? 

A. By the size and velocity of the body. 

Note. — By the centripetal attraction of the Earth, E, the 
Moon, M, is retained in the curve MO. The satellites of 
Jupiter, Saturn, and the Georgium Sidus, all move in ellipj|* 
cal orbits, by this law. See Plate I. Fig A. 

Note. — Thus the Moon, m, by centrifugal force endeavors 
to move in the line m t, but that force is counteracted by the 
centripetal attraction of the Earth E : the other satellites all 
endeavor to recede by the same law, but are made to move 
round their primaries by centripetal attraction. See Plate I. 
Fig A. 



10 CATECHISM OF 

Q. If the centrifugal force of the Moon were de- 
stroyed, in what direction would it move ? 

A. The Moon would move directly to the Earth. 

Q. How would the planets move ? 

A. If the centrifugal force of the planets were 
taken away, they would fall immediately toward the 
sun. 

Q. What is the proportion ? 

A. Bodies attract one another with forces propor- 
tioned to the quantities of matter which they contain. 



CHAPTER I. 

Astronomy. 

Q. What is Astronomy ? 

A. Astronomy is the science which treats of the 
motions, magnitudes, periods, distances, &e. of the 
celestial bodies. 

Q. From what is the word derived ? 

JL Astronomy is derived from two Greek words : 
aster, a star, and nomos, a law. 

Q. How is astronomy divided ? 

Note. — Attraction decreases as the square of the distance ; 
thus, if a body A be twice the distance from S that B is, the 
square of 2 being 4, the force of attraction at A will be four 
times less than at B, or the attraction at B will be twice as 
great as at A. 

A B S 

0- 

If A be three times the distance B, S, the square of 3 
being 9, the attraction at A will be nine times less than at B ; 
or by dividing 9 by 3, the attraction at B will be three times 
greater than at A. 

A B S 





ASTRONOMY. 11 

A. Astronomy may be divided into pure and physi- 
cal. 

Q. What is pure astromomy ? 

A. Plane, or pure astronomy, treats of the planetary 
motions, &c, without any allusion to the cause. 

Q. What is physical astronomy ? 

A. Physical astronomy contains the causes of the 
motions, periods, eclipses, &c. of the heavenly bodies, 
founded on the laws of gravitation. 

Q. What is its use ? 

A. On astronomy are founded Navigation and Dial- 
ling ; without the former, our geographical know- 
ledge and commercial interests would by very limi- 
ted. 



CHAPTER n. 

History of Astronomy* 



Q. Is Astronomy of great antiquity ? 

A, Astronomy was cultivated by the Chinese, 
Egyptians, Chaldeans, Greeks, and Indians, many 
centuries before the Christian era. 

Q. Who were the most celebrated astronomers of 
antiquity ? 

A, The astronomers of antiquity were Pythagoras, 
Ptolemy, and other Egyptians, Tycho Brahe, and 
Copernicus. 

Q. What was the system of Pythagoras ? 

A. In the Pythagorean system the sun was placed 
in the centre, round which the planets and comets 
were supposed to move from west to east in elliptical 
orbits. 

Q. What planets were then discovered ? 



12 CATECHISM OF 

A. The planets known in the time of Pythagoras, 
were Mercury, Venus, the Earth, Mars, Jupiter, and 
Saturn. 

Q. About what time did Pythagoras flourish? 

A. Pythagoras Nourished about 590 years before 
the Christian era. 

Q. In what order did Ptolemy consider the planets 
arranged ? 

A. Ptolemy supposed the Earth to be at rest in the 
centre, and round it moved the Moon, Mercury, 
Yenus, the Sun, Mars, Jupiter, and Saturn, in circu- 
lar orbits, once every day. 

Q. About what time did Ptolemy flourish ? 

A. Ptolemy, the Egyptian philosopher, flourished 
130 years before the Christian era. 

Q. What other systems did the Egyptians receive ? 

A. To account for the phases of Mercury and Venus, 
the Egyptians supposed the Earth to be immovable 
in the centre ; then the Moon and the Sun, round 
which moved Mercury and Venus ; and round the 
whole, Mars, Jupiter, and Saturn. 

Q. What was the system of Copernicus ? 

A. Copernicus revived the doctrine of Pythagoras ; 
and, with the discoveries of Herschel, Olbers, Piazzi, 
Harding, &c, and the proofs adduced in the Newto- 
nian philosophy, this system is now universally re- 
ceived. 

Q. Who was Copernicus ? 

A. Copernicus was a native of Poland, and flourish- 
ed a.d. 1530. 

Q. What was the system of Tycho Brahe ? 

A, In the Tychonic theory the Earth was supposed 
the centre of the Sun and Moon ; Mercury, Venus, 
Mars, Jupiter, and Saturn, revolved about the Sun ; 
while the Sun and planets moved round the Earth 
once in 24 hours. 

Q. Who was Tycho Brahe ? 



ASTRONOMY. 13 

A. Tycho Brahe was a Danish philosopher, and 
flourished a.d. 1586. 

Q. What planets have since been discovered ? 

A. Since the death of Tycho Brahe, five primary 
planets have been discovered, viz. Herschel, Vesta, 
Juno, Ceres and Pallas. 

THE SOLAR SYSTEM. 

Q. Of what does the Solar system consist ? 

A. The solar system consists of the Sun and 11 
planets, viz., Mercury, Yenus, the Earth, Mars, Yesta, 
Juno, Ceres, Pallas, Jupiter, Saturn, and Herschel. 

Q. How many secondary planets are there ? 

A. There are 18 satellites, or secondary planets, 
viz., the Moon, four satellites of Jupiter, seven of 
Saturn, and six of Herschel. 



CHAPTER HI. 

The Sun. 



Q. What is the Sun ? 

A. The Sun is a body nearly globular, placed in 
the centre of the solar system, and is the source of 
light, heat and animation. 

Q. What is his supposed substance, and how is 
light produced ? 

A. Dr. Herschel supposes the Sun to be a solid 
opaque body, surrounded by an extensive lucid, and 

Note. — Vesto, Juno, Ceres, and Pallas, are by some called 
asteroids, or minor planets j Mercury and Venus are called 
inferior, being between the Sun and the Earth j and the rest 
superior. 

2 



14 CATECHISM OF 

transparent atmosphere, of a phosphoric nature, by 
which light is generated. 

Q. What is the velocity of light? 

A. It moves 200,000 miles in a second. 

Q. How far is the Sun distant from the Earth ? 

A. The Sun is 95,000,000 of miles distant from the 
Earth. 

Q. What is the length of the Sun's diameter? 

A. The equatorial diameter of the Sun is 883,246 
miles, and the polar a little less. 

Q. What is his circumference ? 

A. The Sun's circumference is 3,774,692 miles. 

Q. How many times is he larger than the Earth ? 

A. The Sun is 1,402,344 times greater than the 
Earth. 

Q. How many motions has the Sun ? 

A. The Sun has two real and two apparent motions. 

Q. AVhat are the real motions ? 

A. The first motion of the Sun is a small circular 
motion round the centre of all the planets. 

Q. What is the cause ? 

A. The motion is occasioned by the various attract- 
ions of the surrounding planets. 

Q. What is the second real motion ? 

A. The Sun turns upon its axis once in 25 days 10 
hours. 

Note. — To find how many times one planet is greater than 
another : 

Bule. — Cube the diameter of each planet and divide the 
greater number by the less, the quotient will give the propor- 
tional magnitudes, or the number of times one is greater 
than the other. 

To find how many times the Sun is greater than the Earth : 

The Earth's diameter is 7,914 miles, and the Sun's diame- 
ter 885,824; the cube of 7,914 is 49,564,155,684, and the 
cube of 885,824 is 695,092,060,440,746,224; which divided 
by 49,564,155,684, gives the quotient 1,402,344, so that the 
Sun is 1,402,343 times greater than the Earth. 



ASTRONOMY. 15 

Q. What is the use of his diurnal motion ? 

A. It seems probable that the Sun's diurnal motion 
is to throw off centrifugal light though the zodiac, 
giving annual and diurnal motion to the planets. 

Q. What are the apparent motions of the Sun ? 

A. The Sun's first apparent motion is the diurnal 
motion from east to west. 

Q. What is the cause ? 

A. This motion arises from the real motion of the 
Earth upon its axis. 

Q. What is the second ? 

A. The second is the Sun's apparent annual motion 
in the ecliptic. 

Q. What is the cause ? 

A. %he Sun's apparent annual motion arises from 
the Earth's motion in its orbit. 

Q. Has the Sun any other motion ? 

A. Dr. Herschel is of opinion, that the Sun and 
the planets have a general motion with regard to the 
fixed stars. 

Q. In what direction is this general motion ? 

A. This general motion of the sun and planets is 
supposed to be toward the constellation Hercules. 

Q. What is the supposed height of the Sun's atmos- 
phere ? 

A. Dr. Herschel is of opinion, that the Sun's atmos- 
phere is not less than 1,843 miles in height. 

Q. What are the solar spots ? 

A. The spots often observed on the Sun are sup- 
posed to be his dark body seen through rarified parts 
of his atmosphere. 

Q. Was not the Sun formerly supposed to be a body 
of fire? 



Note. — A spectator in the Sun would see the Earth appa- 
rently move from west to east, for the same reason that we 
see the Sun move from east to west. 



16 CATECHISM OF 

A. The Sun was formerly supposed to be a body 
of fire ; but experience has proved, not only the tops 
of the mountains, but the upper regions of the 
atmosphere, to be intensely cold. 

Q. Is the Sun supposed to be inhabited ? 

A, From the similarity to the Earth and the other 
planets, with regard to atmosphere, diversity of sur- 
face, &c, there is every reason to believe that the 
Sun may be inhabited. 



i CHAPTER IV. 

Eclipse of the Sun. 

Q. What is a solar eclipse ? 

A, A solar eclipse is a partial darkness, which is 
occasioned when the Moon comes between the Sun 
and the Earth, and is either total or partial. See 
Plate II. Fig. m. 

Q. What is a total eclipse ? 

A. A total eclipse of the Sun, is when his whole 
face is obscured by the opaque body of the Moon. 

Q. Do total eclipses often happen ? 

A. Total eclipses of the Sun are very rare, and can 
only happen when the Moon is nearest the Earth, or 
in one of the nodes. 

Q. What is a partial eclipse ? 

A. A partial eclipse of the Sun takes place when 
only a part of his surface is darkened. 

Q. What is meant by an annual eclipse ? 

A. An annual eclipse is a partial central eclipse, 
when the Earth is at a distance, and the Moon has 
a luminous ring round her body. 

Q. What is the ring ? 



ASTRONOMY. 17 

A. The luminous ring round the Moon, in a central 
partial eclipse, is the body of the Sun, not able to 
cover, so as to obscure the whole Moon's disc. 

Q. Do solar eclipses happen often ? 

A. Solar eclipses happen much more frequently 
than those of the Moon, in the proportion of three 
solar to one lunar. 

Q. How is it that they are not so often seen ? 

A. Solar eclipses are not visible at one place so fre- 
quently as lunar eclipses, because a lunar eclipse is 
visible to half the globe, whereas a solar eclipse is 
visible to only a small part. 

Q. How is the size of an eclipse measured ? 

A. The whole diameter of the Sun is divided into 
12 parts, called digits, and the Sun is eclipsed so 
many digits as the Moon covers. 

Q. When do they happen ? 

A. An eclipse of the Sun can only happen at the 
change of the Moon, or when she is in conjunction. 

Q. What is the greatest number of eclipses that 
can happen in a year ? 

A. Seven ; and in that case five will be solar and 
two lunar. 

Q. What is the least number that can happen in a 
year ? 

A. Two ; and these must both be solar. 



CHAPTER V. 

Mercmy. 

Q. What is Mercury ? 

A. The planet Mercury is the nearest to the Sun, 
and has a bright blue appearance. 
Q. What is the length of its diameter? 

2* 



18 CATECHISM OF > 

A. The diameter of Mercury is 3,130 English miles. 

Q. What is its circumference ? 

A. The circumference of Mercury is 9,837 miles. 

Q. How far is it distant from the Sun ? 

A. The distance, of Mercury from the Sun is 3G, 
774,320 miles. 

Q. What is its size compared with the Earth ? 

A. The Earth is 16£ times greater than Mercury. 

Q, Does Mercury turn on its axis ? 

A, Mercury turns on its axis in 24 hours 5 minutes 
and 28 seconds. 

Q. In what time does Mercury revolve round the 
Sun? 

A. The annual revolution of Mercury round the 
Sun, is performed in 87 days 23 hours 15 minutes 
and 44 seconds of time. 

Q. At what rate does it move per hour. 

A. Mercury moves at the mean rate of 109,442 
miles per hour. 

Q. What is its eccentricity ? 

A. The eccentricity of Mercury is 7,424,424 miles. 

Q. What is meant by the phases of Mercury ? 

A. Mercury has changes, like the Moon : it is some- 

Note. — To find the distances of the planets from the Sun. 

Rule. — As the square of the Earth's period of revolution 
round the Sun is to the cube of its distance, so is the square 
of any other planet's annual period of revolution to the cube 
of its distance ; and the cube root of the number thus found, 
will be the planet's distance from the Sun. 

To find the distance of Mercury from the Sun, its period 
being 88 days : 

The square of 365 is 133,225. 
The cube of 95 is 857,375. 
The square of 88 is 7,744. 
As 133,225 : 857,375 : : 7,444: 49,836, and the cube root of 
49,836 is 36 3-4 millions of miles. 

In the same manner may be found the distance of the 
other planets from the Sun. 



* ASTRONOMY. 19 

times horned, sometimes gibbous, but never quite 
full. 

Q. Why does the face or disc of Mercury never 
appear full ? 

A. Mercury never appears full to us, because the 
full enlightened side is never turned towards us, ex- 
cepting when it is lost in the Sun's beams. 

Q. What do the phases demonstrate ? 

A. The phases of Mercury clearly prove, that the 
planet is dark or opaque of itself, without the light 
of the Sun. 

Q. What is meant by the transit of Mercury? 

A. When Mercury is between the earth and the 
Sun, it appears on the Sun's disc as a dark speck, 
which is called a transit. 

Q. How would the Sun appear to a spectator in 
Mercury ? 

A. The Sun would appear to a spectator in Mercury 
seven times larger than it does to us. 



CHAPTER VI. 

Venus. 

Q. What is Venus ? 

A. Venus is the most brillliant of all the planets, 
and may sometimes be seen at noonday. 

Q. What is the length of its diameter ? 

A. The diameter of Venus is 8,600 miles. 

Q. What is the circumference of Venus? 

A. The circumference of Venus is about 27,000 
miles, being somewhat larger than the Earth. 

Q. How far is Venus distant from the Sun ? 

A. The distance of Venus from the Sun is 08,716, 
569 miles. 



20 CATECHISM OF 

Q. In what time does it turn on its axis ? 

A, Venus turns round upon her axis in 23 hours 

21 minntes and 7 seconds of time. 

Q. In what time does it preform its orbit ? 

A. Venus moves round the Sun in 224 days 16 
hours 49 minutes 11 seconds. 

Q. At what rate does it move ? 

A. Venus moves at the rate of 80,062 miles per hour. 

Q. What is her eccentricity ? 

A. The eccentricity of Venus is 492,000 miles 

Q. Has Venus phases, like Mercury ? 

A. Venus, like Mercury, has phases similar to the 
Moon. 

Q. What is a transit of Venus ? 

A, Transit of Venus is produced by the planet 
passing between the Earth and the Sun. 

Q, Are the transits of Venus frequent ? 

A. The transits of Venus are rare, but of greater 
utility in Astronomy, than those of Mercury. 

Q. What do the transits of Venus illustrate ? 

A. From a transit of Venus the Sun's true parallax 
has been ascertained. 

Q. What is the use of the Sun's true parallax ? 

A. From the Sun's true parallax astronomers have 
been enabled to ascertain the Earth's distance from 
the Sun, as also the distances of the other planets. 

Q. What else has been learned from observing the 
transits of Venus ? 

A. The atmosphere of Venus was observed to throw 
a shade on the Sun's disc about 5 seconds before the 
body of Venus touched his edge. 

Q. What is its height ? 

A. The height of the atmosphere of Venus has 
been calculated to be 50 miles. 

Q. When was this phenomenon first observed ? 

A. Venus was first observed to pass over the Sun's 
disc, Nov. 16, a. d. 1639. 



ASTRONOMY. 21 

Q. When will the next transit happen ? 

A. There will be only two transits of Venus in the 
present century ; the first December 8th, 1874 ; and 
the second in 1882. 

Q. What will the size of the Sun be to a spectator 
in Yen us ? 

A. The Sun will appear twice as large to an inhabi- 
tant of Venus as to us ; Mercury will be a morning 
and evening star to tltem, as Venus is to us. 

Q. When is Venus called the morning star ? 

A. When it is in the upper part of its orbit, and 
rises before the Sun. 

Q. When is Venus called the evening star ? 

A. When it passes round into the lower part of its 
orbit, and sets after the Sun. 

Q. How long is Venus an evening, and how long 
a morning star ? 

A. Venus is 290 days an evening star, and a morn- 
ing star somewhat longer. 

Q. What else is worthy of notice in this planet ? 

A. Venus has exhibited bright and dark spots on 
her disc, and the mountains are six times higher 
than any on our globe. 

Q. Where is her orbit ? 

A. Venus moves immediately within the orbit of 
the Earth. 



CHAPTER VII. 

The Earth. 



Q. What is the Earth ? 

A. The Earth is the third planet from the Sun ; and 
its orbit is next above that of Venus. 
Q. Of what does it consist ? 



22 CATECHISM OF 

A. The Earth is a solid body of terr.es tial matter, 
nearly globular. 

Q. What is the length of its diameter ? 

A. The equatorial diameter of the Earth is 7,024 
miles, and the polar about 37 miles shorter. 

Q. What is the circumference ? 

A. The Earth's circumference round the equator is 
24,904 miles, and through the poles 24,773 miles. 

Q. Does this flatness at the pfrles make any differ- 
rence in bodies moved from either of them to the 
equator ? 

A. The weight of bodies is increased when taken 
from the equator toward the poles ; if a body of 
the weight of one pound at the equator, was taken 
to either pole, it would weigh 1,00569 pounds. 

Q. What is the cause of this change in gravity ? 

A. The equator being farther from the Earth's 
centre than either of the poles, the centripetal force 
is greatest at the equator. 

Q. Has this difference any effect on the vibration 
of pendulums ? 

A. Pendulums of the same length vibrate lower at 
the equator than at the poles. 

Q. How is this remedied ? 

A. By making the pendulum longer or shorter ; 
thus, one to vibrate seconds at the equartor, must be 
39 inches long, and at the poles 39,209 inches. 

Q. How far is the Earth from the Sun ? 

A. The distance of the Earth from the Sun is 
95,000,000 miles. 

Q. In what time does the light come from the Sun 
to the Earth ? 

A. The light of the Sun occupies 8 minutes 7J 
seconds in coming to the Earth. 

Q. How many motions has the Earth? 

A. Two : the diurnal, and the annual, or the daily 
and the yearly. 



ASTRONOMY. 23 

Q. What is meant by the Earth's annual motion ? 

A. The Earth's annual motion is her revolution 
round the Sun. 

Q. What does this produce ? 

A. The Earth's annual motion produces the changes 
of the season, viz. : Spring, Summer, Autumn, and 
Winter. 

Q. In what time does the Earth preform a revo- 
lution round the Sun ? 

A. The Earth performs an annual revolution in 
365 days and 6 hours. 

Q. At what rate does she move in her orbit ? 

A. The Earth moves round the Sun at the rate of 
00,000 miles per hour. 

Q. What is the eccentricity of the Earth's orbit ? 

A. The Earth's eccentricity is 1,618,000 miles. 

Q. In what time does the Earth turn on her axis ? 

A. The Earth turns upon her axis once in every 
24 hours. 

Q. What changes does this produce ? 

A. The Earth's rotation on her axis produces the 
change of day and night. 



CHAPTER VIII. 

The Moon. 

Q. What is the Moon ? 

A. The Moon is an opaque body, nearly globular, 
and receives her light from the Sun. 

Q. What is the use of the Moon ? 

A. The Moon is a satellite to the Earth, and par- 
tially supplies us with light in the absence of the 
Sun. 



24 CATECHISM OF 

Q. Of what size is the Moon ? 

A. The Moon is about one fifteenth part of the size 
of the Earth; her diameter being 2,180 miles, and 
her circumference 6,851 miles. 

Q. How far is she from the Earth ? 

A. The Moon moves at the distance of 240,000 
miles from the Earth. 

Q. How far is the Moon distant from the Sun ? 

A. The Moon's mean distance from the Sun in 
miles is 95,000,000. 

Q. In what time does the Moon turn on her 



axis 



? 



A. The Moon performs a rotation on her axis in 
27 days 7 hours 43 minutes and 8 seconds. 

Q, In what time does the moon preform her orbit ? 

A. The Moon performs her orbit exactly in the 
same time that she goes round the Earth. 

Q. At what rate does she move ? 

A. The Moon moves in her orbit at the rate of 
2,290 miles per hour. 

Q. What is the length of her day and night ? 

A. The lunar day and night, taken together, are 
the same as our lunar month, viz. : 27 days 7 hours 
43 minutes and 8 seconds. 

Q. On what physical cause does the Moon's motion 
depend ? 

A. The Moon's motion is produced by the mutual 
attraction between the Earth and the Moon. 

Q. What is meant by the Moon's phases ? 

A. The phases of the Moon are those changes 
which we observe in her shape ; she is sometimes 
full, sometimes horned, and at other times gib- 
bous, according as her dark side is turned toward us. 

Q. When is it new Moon ? 

A. When the Moon is in conjunction, or between 
the Earth and the Sun, and the dark side is presented 
to us. 



ASTRONOMY. 25 

Q. When is it full Moon ? 

A. When the Moon is in opposition, or when the 
Earth is between the Sun and the Moon, and the 
illuminated side is presented to us. 



CHAPTER IX. 

Eclipses of the Moon. 



Q. "What is meant by an Eclipse ? 

A. An eclipse of the Moon is the privation of the 
Sun's light, occasioned by the dark body of the 
Earth coming between the Sun and Moon. 

Q. When do they happen ? 

A. Eclipses of the Moon can never happen but 
when the Moon is full. 

Q. Why can they not happen ? 

A. Eclipses of the Moon can only happen at full 
moon, because the Sun and Moon are only then in 
opposition. 

Q. Why do eclipses not happen every opposition 
and conjunction. 

A. The Moon is not always eclipsed when full, be- 
cause her orbit does not coincide with the plane of 
the ecliptic at every opposition and conjunction. 

Q. What is a partial eclipse ? 

A. A partial eclipse is when only a part of the 
Moon's face falls within the dark "shadow of the 
Earth. 

Q. What is a total eclipse ? 

A. A total eclipse happens when the shadow of the 
Earth covers the whole disc of the Moon. 

Q. In what direction does an eclipse commence ? 

A. The dark shadow of the Earth begins at the 
3 



26 CATECHISM OF 

eastern side of the Moon, and leaves her on the 
west. 

Q. On what does the obscuration depend ? 

A. The obscuration is either partial or total, ac- 
cording to the Moon's distance from the earth. 

Q. How long do eclipses last ? 

A. The conical shadow of the Earth is sometimes 
more than three hours in passing over the Moon's 
disc. 

Q. What is remarkable in the Harvest Moon ? 

A. The Moon when full in harvest rises several 
successive nights sooner after sunset, and with less 
difference of time, than at any other, full Moon during 
the year. 

Q. What is the cause ? "' ^ 

A. The Moon rises for several nights nearly alike 
early, because she is full in the signs Pisces and 
Aries, while the Sun is in the opposite signs Yirgo 
and Libra. 

Q. How does this occasion a difference ? 

A. When the Sun is in Yirgo and Libra, the op- 
posite part of the ecliptic rises from the horizon in 
our latitude with a smaller angle. 

Q. Why does this make so material a difference ? 

A. Pisces and Aries rising with a smaller angle, 
make the Moon move through a smaller space in a 
shorter time than she would through a large space. 

Q. Why is not this always the case at full Moon ? 

A. The Moon would rise with less difference of 
time, as in Autumn, if the Moon's orbit lay in the 
the plane of the ecliptic. 

Q. Why is not this the same in Winter, when the 
Moon is in Pisces and Aries ? 

A. The equality of the Moon's rising in winter is 
not observable, because she is then in her first quar- 
ter and rises about noon when the Sun is above the 
horizon. 



ASTRONOMY. 27 

Q. Why does it not happen in Spring? 

A. In Spring the Moon is in those signs at her 
change when rising with the Sun she gives no light. 

Q. Why does not this happen in Summer ? 

A. In Summer the Moon is in Pises and Aries, in 
her last quarter, and rising at midnight, is not 
noticed. 

Q. Are these appearances always alike in the har- 
vest Moons ? 

A. The harvest Moons are not every year alike, but 
they go through a periodical change every 19-years; 
sometimes more, and at other times less beneficial 
to the harvest, which may be more easily illustrated 
on a celestial globe. 



CHAPTER X 
Mars. 



Q. Where is Mars situated ? 

A. Mars is situated next without the orbits Df the 
Earth and Moon. 

Q. What is the appearance of Mars ? 

A. Mars is of a dusky red color, owing to the den- 
sity of its atmosphere. 

Q. What is its diameter ? 

A. The equatorial diameter of Mars is 4200 miles, 
and its polar diameter 3931 miles. 

Q. What is its circumference? 

A. The circumference of Mars is 13,200 miles. 

Q. In what time does it preform its orbit ? 

A. Mars moves round the Sun in 686 days 23 home 
30 minutes and 39 seconds. 

Q. At what rate does it move ? 



28 CATECHISM OF 

A. Mars moves round the Sun at the rate of 55,166 
miles per hour. 

Q. In what time does it turn on its axis ? 

A. Mars turns once round its axis in 24 hours 39 
minutes and 21 seconds. 

Q. How far is Mars distant from the Sun ? 

A. Mars is distant from the Sun 244,760,806 miles. 

Q. What is its eccentricity ? 

A. The eccentricity is Mars is 13,463,000 miles. 

Q. Has Mars any atmosphere? 

A. Dr. Herschel is of opinion, that the atmosphere 
of Mars is very considerable. 

Q. Has Mars any phases ? 

A. Mars increases and decreases like the Moon, 
but never appears horned. 

Q. What may be deduced from this ? 

A. The appearance of Mars clearly demonstrates, 
that it shines by means of solar light. 

Q. How would the Earth appear to an inhabitant 
of Mars ? 

A. The Earth would appear to a spectator in Mars, 
like a star, or as Venus does to us. 

Q. Has Mars any satellites ? 

A. Mars has no satellites as yet observed. 



CHAPTER XI. 

Vesta. 



Q. What is Vesta ? 

A. Vesta is one of the four minor planets, or aste- 
roids. 

Q. What is the appearance of Vesta ? 

A. Vesta shines with a purer light than any of the 
minor planets. 



ASTRONOMY. 29 

Q. Is this planet ever visible without glasses ? 

A. Vesta is often seen in a clear evening, without 
the aid of the telescope : her appearance is similar 
to that of the Georgium Sidus, or of a star of the 
fifth magnitude. 

Q. Where does Vesta move ? 

A. The orbit of Vesta is between that of Mars and 
Ceres. 

Q. How far is Vesta distant from the Sun ? 

A. Vesta is distant from the Sun 225,435,000 miles. 

Q. In what time does it perform a revolution ? 

A. Vesta performs a revolution round the Sun in 
1,335 days 4 hours 55 minutes and 12 seconds. 

Q. At what rate does it move ? 

A. Vesta moves 44,202 miles every hour. 

Q. What is the eccentricity of this planet ? 

A. The eccentricity of Venus is 21,015,053 miles. 

Q. When was Vesta discovered ? 

A. Vesta was discovered early in the year 1807. 

Q. By whom was Vesta discovered ? 

A. Vesta was discovered by Dr. Olbers, a physi- 
cian, of Brunn, in Germany. 

Q. When was she first observed in England ? 

A. In England, Vesta was first observed at Black- 
heath, by Mr. Groombridge, April 26, 1807. 

Q. Is there any thing remarkable in the orbit of 
Vesta? 

A, The orbit of Vesta cuts the orbit of Pallas, but 
not where it is cut by Ceres. 



3* 



30 CATECHISM OF 

CHAPTER XII. 

Juno. 

Q. Where is Juno situated ? 

A. Juno, one of the minor planets, moves between 
the orbits of Vesta and Pallas. 

Q. What is its size ? 

A. The diameter of Juno is about 1,400 miles. 

Q. What is its appearance ? 

A. Juno is of a reddish color, but free from that 
nebulosity which surrounds Pallas. 

Q. Has Juno any atmosphere ? 

A. Schroeter is of opinion, that the atmosphere of 
of Juno is more dense than any of the planets ; but 
it is sometimes very brilliant. 

Q. To what may the changes be attributed ? 

A. The planet Juno appears sometimes very bril- 
liant, owing to certain changes in the density of its 
atmosphere. 

Q. How far is Juno from the Sun ? 

A, The distance of Juno from the Sun is 253,380,485 
miles. 

Q, In what time does it perform its orbit ? 

A. Juno moves round the Sun in 1,590 days 23 
hours and 57 minutes. 

Q. At what rate does it move ? 

A. Juno moves at the rate of 41,170 miles every 
hour. 

Q. What is its eccentricity ? 

A. The eccentricity of Juno is 68,588,343 miles. 

Q. When and by whom was Juno discovered ? 

A, On the 1st of September, 1804, Juno was first 
discovered by Mr. Harding, of Lilienthal, in the 
neighborhood of Bremen. 



ASTRONOMY. 31 

CHAPTER XIII. 

Ceres. 

Q.- "What is the appearance of Ceres ? 

A. The planet Ceres appears like a star of the sixth 
magnitude, and has a ruddy appearance. 

Q. What is the cause of this ruddy appearance ? 

A, Ceres exhibits a ruddy appearance, because it 
is surrounded by a dense atmosphere subject to 
numerous changes. 

Q. What is the supposed height of the atmosphere ? 

A. The atmosphere of Ceres, according to Schroeter, 
is 676 miles in height ; and, like that of the Earth, it 
becomes gradually thinner toward the top. 

Q. When and by whom was Ceres discovered ? 

A. The planet Ceres was first seen January 1st, 
1801, by M. Piazzi, of Palermo. 

Q. What is the diameter of Ceres ? 

A. Schroeter makes the diameter of Ceres to be 
1624 miles, while Dr. Herschel reckons it only 160 
miles. 

Q. How is this difference accounted for ? 

A. The German astronomer Schroeter maintains 
that the micrometer used by Herschel was placed too 
far from the eye, and that only the clear part of the 
nucleus of the planet had been measured. 

Q. What is the distance of Ceres from the Sun ? 

A. The distance of Ceres from the Sun is 262,903,570 
miles. 

Q. In what time does Ceres move round the Sun ? 

A. Ceres moves round the Sun in 1681 days 2 
hours and 56 minutes. 

Q. At what rate does Ceres move ? 

A. Ceres moves round the Sun at the rate of 40,930 
miles per hour. 



32 CATECHISM OF 

Q. What is the eccentricity of this planet ? 
A. The distance of the centre from the foci of the 
elliptical orbit of Ceres, is 20,598,130 miles. 
Q. Where does Ceres move ? 
JL The orbit of Ceres is without that of Juno. 



CHAPTER XIV. 

Pallas. 



Q. When and by whom was Pallas discovered ? 

A. The planet Pallas was discovered March 28th, 
1802, by Dr. Olbers, at Bremen, in Lower Saxony. 

Q. What is the appearance of Pallas ? 

A. Pallas is less ruddy than Ceres, owing to the 
smaller extent of atmosphere and nebulosity. 

Q. What is the height of the atmosphere ? 

A. The atmosphere of Pallas is 468 miles in height, 
and undergoes similar changes to Ceres ; but her 
light is exhibited in great variations. 

Q. What is the size of this planet? 

A. Pallas, according to Schroeter, is 2099 miles in 
diameter, but, according to Herschel, 80 miles. 

Q. What is the distance from the Sun ? 

A. The distance of Pallas from the Sun is 266,000,000 
miles. 

Q. In what time does Pallas perform a revolution ? 

A. Pallas revolves round the Sun in 1681 days 17 
hours and 1 minute. 

Q. At what rate does Pallas move ? 

A. Pallas moves round the Sun at the rate of 40,930 
miles per hour. 

Q. What is the eccentricity of this planet ? 

A. The eccentricity of Pallas is 64,516,673 miles. 



ASTRONOMY. 33 

Q. Is there any thing remarkable in this planet ? 
A. The orbit of Pallas crosses that of Ceres. 
Q. How does this happen? 

A. Ceres crosses the orbit of Pallas, owing to the 
great eccentricity of the latter. 



CHAPTER XV. 

Origin of Ceres, Pallas, Juno, and Vesta. 

Q. "What is the supposed origin of the four minor 
planets ? 

A. Some have supposed them to have been origin- 
ally one planet. 

Q. What leads to this conjecture? 

A. The great space between the orbits of Mars and 
Jupiter does not, without another planet, seem to 
agree with the harmony of proportionable distance 
in the solar system. 

Q. How is this accounted for ? 

A. The four minor planets are supposed to have 
been separated from one original planet, by some 
convulsion in nature, capable of destroying the mu- 
tual attraction of the fragments ; such as an earth- 
quake. 

Q. How are we to expect to find these fragments, 
according to this theory ? 

A. It is evident, that the smaller parts would, by 
the explosive force, be thrown to the greatest distance 
from the original orbit, while the greater fragments, 
on account of their gravity, would deviate less from 
the original path of the primitive body. 

Q. Is this the case with the new planets ? 

A. Pallas and Juno are, on account of their eccen- 
tricity, supposed to be smaller then Ceres and Vesta. 



34 CxVTECHISM OF 

Q. Does this theory explain any other phenomena 
in nature ? 

A. This theory has furnished us with evidence, 
that the meteoric stones commonly called thunder- 
bolts, may be the smaller fragments of an original 
planet. 

Q. How is that possible ? 

A. The cohesive force of the planet being destroyed 
by the explosive force, a number of smallar frag- 
ments would be precipitated with great velocity, 
without the sphere of the planet's attraction. 

Q. Would not these smaller fragments be attracted 
by Mars, and fall toward that planet rather than 
toward the Earth ? 

A. The meteoric stones might be precipitated with- 
in the sphere of the Earth's attraction, when Mars 
was at a remote part of its orbit. 

Q. When within the sphere of the Earth's attrac- 
tion, how would they move ? 

A. The fragments thus precipitated within the 
sphere of the Earth's attraction, might revolve round 
it at different distances. 

Q. What would occasion their fall ? 

A. The meteoric stones might fall from a diminu- 
tion of their centrifugal force, or by being struck 
with electric fluid. 

Q. What is their particular substance ? 

A. The meteoric stones are principally composed 
of iron ; those found in South America and Siberia 
are masses of melted iron, and possessed of magnetic 
virtue. 

Q. From what part of the planet are they supposed 
to be precipitated ? 

A. From the internal density and magnetism of 
the Earth, we are led to conclude, that the central 
part, and greater part of the Earth is either iron, 
stone, or melted metals, which have the power of 



ASTRONOMY. 35 

magnetism, and the meteoric stones are found to be 
iron ore. 

Q. How is this applicable to meteoric stones? 

A. When an internal explosion takes place in a 
planet, the central parts of the planet's substance 
must be thrown to the greatest distance ; and, from 
their similarity to our Earth, we have every reason 
to suppose the meteoric stones to have been precipi- 
tated from the planet's centre. 



CHAPTER XVI. 

Jupiter. 

Q. Where is Jupiter situated ? 

A Jupiter's orbit is between those of Pallas and 
oaturn. 

Q. What is its size ? 

A. Jupiter, the largest of all the planets, is more 
than a thousand times larger than the Earth. 

Q. What is its diameter? 

A. The eqatorial diameter of Jupiter is 91 000 
miles and itspolar diameter 6000 miles shorter' 

<*>. What is its distance from the Sun ? 

A Jupiter is distant from the Sun 49? ^65 155 
miles. ,-^,1^ 

Q. In what time does it perform its orbit ? 

A. Jupiter moves round the Sun in 4332 davs 14 
hours and 19 seconds. y 

Q. At what rate does it move ? 

A. Jupiter in his orbit round the Sun moves at the 
mean rate of 298,660 miles per hour. 

Q. In what time does it turn on its axis ' ? 

A. Jupiter turns round on its axis in 9 hours 55 
minutes and 50 seconds. 



36 CATECHISM OF 

Q. At wha^rate does it move ? 
A. The equatorial parts of Jupiter, in revolving on 
its axis, is about 26,000 miles per hour. 
Q. Is there any difference of season in Jupiter ? 
A. Jupiter's axis being perpendicular, or having 
no inclination, it can have no difference of seasons. 
' Q. What is the length of its day ? 
A. The length of the day in Jupiter is five hours 
and its night the same. 
Q. What is the state of the polar regions ? 
A. In the polar regions of Jupiter there is perpetual 
winter. 
Q. What is the state of the parts near the equator/ 
A. About the equator of Jupiter is perpetual sum- 
mer. . 
Q. What are the belts of Jupiter ? 
A. The belts, or zones, are faint substances seen 
on the body of Jupiter, and supposed to be clouds 
floating in its atmosphere. 
Q. How many belts are there? 
A. The belts of Jupiter are always parallel to its 
equator ; the number is variable ; sometimes eight 
may be seen, at other times only one. 
Q. What are the spots seen in those belts ? 
A. The dark spots seen on the surface of Jupiter, 
are supposed to be clouds more dense than the ring ; 
and, when the belts disappear, the spots vanish also. 
Q. About what time do they generally continue ? 
A. The spots on the belts of Jupiter, sometimes 
continue the same for three months: at other times - 
new ones spring up during observation. 

Q. Are they all supposed to be clouds floating in 
its atmosphere ? , 

A. There is one large spot which has been observea 
to continue for three years together, and is supposed 
to be a part of the body of Jupiter, seen through a 
rarified part of its atmosphere. 



ASTRONOMY. 37 

Q. What are the uses of these spots ? 
A. By observing these spots, the time of Jupiter's 
rotation on its axis has been found. 



CHAPTER XVII. 

Jupiter 's Satellites? 

Q. How many Satellites has Jupiter ? 

A. Jupiter has four satellites or moons, which move 
round its body from west to east, at different periods 
and distances. See Plate I. Fig. c. 

Q. When and by whom were they discovered ? 

A. In 1610, the satellites of Jupiter were discovered 
by Galileo. 

Q. At what distance is the first ? 

A. The first satellite is distant from the centre of 
Jupiter, 264,490 miles. 

Q. What time does it require to move around its 
primary ? 

A. The first satellite moves round the body of Ju- 
piter in 1 day 18 hours 27 minutes and 23 seconds. 

Q. What is the distance of the second ? 

A. The second satellite is distant from Jupiter 
420,815 miles. 

Q. In what time does it perform a revolution ? 

A. The second satellite of Jupiter performs a revo- 
lution in 3 days 13 hours 13 minutes and 42 seconds. 

Q. What is the distance of the third satellite ? 

A. The third satellite of Jupiter moves at the dis- 
tance of 671,234 miles. 

Q. What is its period. 

A. Jupiter's third satellite performs its orbit in 7 
days 3 hours 42 minutes and 33 seconds. 
4 



38 



CATECHISM OF 



Q. What is the distance of the fourth satellite ? 

A. Ine fourth satellite of Jupiter is distant from 
the centre of that planet 1,180,582 miles. 

Q. In what time does it perform its orbit ? 

A. The fourth satellite of Jupiter performs a 
revolution m 16 days 16 hours 31 minutes and 50 
seconds. 

Q What is the use of the satellites to the inhabi- 
tants of Jupiter ? 

A. The satellites or moons of Jupiter, serve to en- 
lighten that planet, the same as the Moon does the 
Jiiartn. 

Q. Of what use are they to us ? 

A. BJ observing the immersion and emersion of 
Jupiter s satellites, they are of the greatest use in 
fan ding the longitude of places. 

Q. Why are they of use ? 

A. Because the immersion and emersion takes 
place at the same instant of time on every part of 
the Earth's surface. 

Q. Which satellite is best for the purpose ? 
m A. The motion of the first being best known, and 
its eclipses happening more frequently than those 
of the other planets, its eclipses are the best for as- 
certaining the longitude of places. 

Q. How is the longitude found ? 

A. The longitude of any place may be found, by 
taking the difference of the immersion and emersion 
observed from the corresponding time in the Ephe- 
meris ; this time turned into degrees will show the 
distance east or west from Greenwich. 

Q. How is time turned into degrees of distance ? 

A. Time is turned into degrees of distance, by al- 
lowing 15 degrees to every hour of time. 



ASTRONOMY. 39 

CHAPTER XVIII. 

Saturn. 

Q. What is the appearance of Saturn ? 

A. Saturn shines with a pale dead light, on account 
of its vast distance from the Sun. 

Q. What is its size ? 

A. The equatorial diameter @# Saturn is about 
79,000 miles, and its polar diameter about 71,000 
miles. 

Q. What is its circumference ? 

A. The circumference of Saturn is 244,137| miles. 

Q. How far is it distant from the Sun ? 

A. Saturn's distance from the Sun is 906,183,000 
miles. 

Q. In what time does Saturn perform its orbit ? 

A. Saturn moves round the Sun in 10,758 days 23 
hours and 17 minutes, or about 30 years. 

Q. At what rate does it move ? 

A. Saturn moves at the rate of 22,050 miles per 
hour. 

Q. In what time does it turn on its axis ? 

A. Saturn performs a rotation on its axis in 10 
days 16 hours and 19 minutes. 

Q. What is its eccentricity ? 

A. The eccentricity of Saturn's obrit is 49,000,000 
miles. 

Q. Of what nature are the belts or zones seen on 
its disc ? 

A. The zones or belts of Saturn are similar to those 
of Jupiter, and originate from the same«cause. 

Q. What is the supposed cause ? 

A. The zones of Saturn are considered to be clouds 
floating in its atmosphere. 



40 CATECHISM OF 

Q. What kind of atmosphere h as it ? 

A. The atmosphere of Saturn is observed to be 
very dense. 

Q. What else is remarkable in Saturn ? 
-A. Saturn is surrounded by two concentric rings. 

Q. What are these supposed to be ? 

A. Some have supposed the substance of the rings 
to be a vast assemblage of planets ; others have sup- 
posed them to be a permanent bright cloud. Dr. 
Herschel has observe^ that they cast a shadow upon 
the planet. 

Q. What is the use of these rings ? 

A. The rings are supposed to reflect the light of 
the Sun upon the planet Saturn. 

Q. What is the distance of the first from Saturn ? 

A. The first, or inner ring, is distant from Saturn 
21,000 miles. 

Q. What is the breadth of the inner ring ? 

A. The breadth of Saturn's inner ring is 20,000 
miles. 

Q. What is the distance between the two rings ? 

A. The outer ring of Saturn is distant from the 
inner ring 2839 miles. 

Q. What is the breadth of the outer, ring ? 

A. The outer ring of Saturn is 7200 miles broad. 

Q. Are these rings stationary? 

A. The rings of Saturn revolve round its body in 
10 hours and 33 minutes* 

Note. — As this planet revolves around the Sun, one of its 
sides is illuminated during one-half of the year, and the 
other side during the other half; so that, as one of Saturn's 
years is equal to 30 of our years, one-half of his sides will 
be enlightened and darkened, alternately every 15 years. 



ASTRONOMY. 41 

CHAPTER XIX. 

Satellites of Saturn. 

Q. How many satellites has Saturn ? 

A. Saturn has seven satellites, moving at different 
distances from its body. 

Q. What is the distance of the first satellite ? 

A. The first satellite is distant from Saturn 119,627 
miles. 

Q. In what time does it perform a revolution ? 

A. It moves round the planet Saturn in 23 hours 
37 minutes and 23 seconds. 

Q. How far is the second distant ? 

A. The second satellite is distant from Saturn 
153,496 miles. 

Q. What is the time of performing its orbit ? 

A. The second satellite performs its orbit in 1 day 
8 hours 53 minutes and 9 seconds. 

Q. How far is the third distant ? 

A. The third satellite from Saturn moves at the 
distance of 190,044 miles. 

Q. In what time does it perform a revolution ? 

A. Saturn's third satellite performs a revolution in 
1 day 21 hours 18 minutes and 26 seconds. 

Q. What is the period and distance of the fourth ? 

A. The fourth, satellite of Saturn moves round it 
in 2 days 17 hours 44 minutes and 51 seconds, at 
the mean distance of 243,449 miles. 

Q. What is the period and distance of the fifth 
satellite ? 

A. The fifth satellite of Saturn performs its orbit 
in 4 days 12 hours 25 minutes and 11 seconds, at 
the distance of 340,005 miles. 

Q. What is the period and distance of the si^th ? 
4* 



42 CATECHISM OF 

A. The sixth satellite of Saturn performs its orbit 
in 18 days 22 hours 41 minutes and 14 seconds, at 
the mean distance of 788,258 miles. 

Q. What is the period and distance of the seventh? 

A. The seventh and most remote satellite of Saturn 
performs a revolution in 79 days 7 hours 54 minutes 
and 37 seconds, at the distance of 2,297,541 miles. 

Q. Is there any thing to remark on the last satel- 
lite? 

A, The most remote of Saturn's satellites performs 
a rotation on its axis, like our Moon. 

Q. In what time does it perform a revolution on its 
axis ? 

A. The seventh satellite of Saturn turns on its axis 
in the same time that it performs its revolution 
round Saturn, viz. : in 107 days 16 hours 39 minutes 
and 56 seconds. 



CHAPTER XX. 

Herschel, or the Georgium Sidns. 

Q. When and by whom was Herschel discovered ? 

A. Herschel was discovered at Bath, March 13th, 
1781, by Dr. Herschel ; he afterwards discovered its 
six satellites. 

Q. Was Herschel never observed till 1781 ? 

A. Herschel was observed by Flamstead, Mayer, 
and Le Mounier ; but they considered it to be a 
small star. 

Q. Why was it called the Georgium Sidus ? 

A. This name was given to it as a testimony of re- 
spect to George the Third, of England, in whose 
reign it was discovered ; though it is now generally 
called Herschel, in honor of its first discoverer. 



ASTRONOMY. 43 

Q. Where is this planet situated? 

A. Herschel is the most remote planet in the solar 
system. 

Q. What is its appearance? 

A. It shines with a bluish white light, and is sel- 
dom seen without the aid of a powerful telescope. 

Q. What is its distance from the Sun ? 

A. The distance of Herschel from the Sun is 
822,418,976 miles. 

Q. What is its eccentricity ? 

A. The eccentricity of Herschel is 1,800,000,000 
miles. 

Q. What is its diameter ? 

A The diameter of Herschel is 34,170 miles. 

Q. What is the period of its revolution ? 

A. The period of this planet is 30,646 miles per 
hour. r 

Q. At what rate does it move ? 

A. It moves in its revolution round the Sun, at the 
rate of 15,546 miles per hour. 

Q. In what time does it turn on its axis ? 

A. The rotation of Herschel on its axis has not as 
yet been determined, owing to its immense distance 
from the Earth. 



CHAPTEK* XXI. 

Satellites of HerscTiel. 



Q. How many satellites has Herschel ? 

A. It has six satellites. 

Q. Were the satellites discovered the same time as 
the planet ? 

A. The satellites have been discovered since the 
planet by Dr. Herschel, 



44 CATECHISM OF 

Q. What is the period and distance of the first 
satellite of Herschel? 

A. The first satellite of Herschel performs a revo- 
lution in 5 days 21 hours 25 minutes and 21 seconds, 
at the distance of 204,155 miles. 

Q. What is the period and distance of the second ? 

A. The period of the second is 8 days 16 hours 57 
minutes and 47 seconds, at the distance of 290,821 
miles. 

Q. What is the period and distance of the third? r 

A. The third satellite of Herschel performs its orbit 
in 10 days 23 hours 3 minutes and 59 seconds, at the 
distance of 339,052 miles. 

Q. What is the period and distance of the fourth ? 

A. The fourth satellite of Herschel performs its 
orbit in 13 days 10 hours and 56J minutes, at the 
distance of 388,718 miles. 

Q. What is the period and distance of the fifth ? 

A, The fifth satellite moves round Herschel in 38 
days 1 hour and 48 minutes, at the distance of 
777,487 miles. 

Q. What is the period and distance of the sixth 
satellite ? 

A. The sixth satellite of Herschel performs its 
orbit in 107 days 16 hours 39 minutes and 56 seconds, 
at the distance of 1,555,872 miles. 

Q. Is there at any thing remarkable in the motion 
of these satellites ? 

A. The satellites of Herschel are supposed to move 
retrograde, or contrary to the order of the signs. 



ASTRONOMY. 45 

♦CHAPTER XXII. 

Comets. 

Q. What are the Comets ? 

A. The Comets are solid and opaque planetary 
bodies, moving in elliptical orbits, of great eccen- 
tricity. 

Q. From what is the word derived ? 

A. Comet is derived from cometa, hairy ; because 
they generally appear with tails resembling hair 
thrown in an opposite direction to the Sun. 

Q. What is this tail supposed to be ? 

A. The tails of Comets are supposed to be vapors 
arising from the body of the comets by the heat of 
the Sun. 

Q. What is the head or body called ? 

A. The head or solid part of a comet is called the 
nucleus. 

Q. Have the comets any atmospheres ? 

A. The comets are, to appearances, surrounded by 
atmospheres ten times higher than the nucleus. 

Q. Have they any phases ? 

A. Some of the comets have phases like the Moon, 
and recede far beyond the orbits of any known 
planet at their aphelion. 

Q. In what direction do they move ? 

A. Some of the comets move direct in the order of 
the zodiacal signs ; others move retrograde. 

Q. Is their motion regular ? 

A. The motion of the comets is accelerated when 
moving towards, and retarded in going from the 
Sun. 

Q. At what rate do the comets move ? 

A. The comet of 1680, at its perihelion was sup- 
posed to move at the rate of 880,000 miles per hour. 



46 CATECHISM OF 

Q. How near did that comet approach the Sun ? 

A The comet of 1680 approached within 130 000 
miles to the surface of the Sun. ^v,uuu 

Q. Are the comets numerous? 

A. About 500 comets have, at different periods 
W 2SS& ^ thG el — ts <*>*«* «5j have 

?' ™I n nn r did the ? a PProach to the Sun ? 
n f; Of the 90 comets, 22 passed between Mercury 
and the Sun 40 between Venus and Mercury 17 
between the Earth and Venus, 16 between the Earth 

^ ^ a J S ' . and 4 befcween Mars and Jupiter 

a rmT at 1S the su PP osed 8i ze of comets ? 

A. They are of different magnitudes ; the greater 
number are supposed to be less than the Moon 

a Ix n th ^ su PP° sed len gth of their tails ? 

nf 1811 COm , etS in len ^ th are ^rious ; that 

of 1811 was computed to be 33,000,000 miles long. 

CHAPTER XXIII. 

Fixed Stars. 

Q. What are the fixed stars ? 
_ A. The fixed stars are those bodies which appear 
s n stem mmenSltJ SpaCG far bey ° nd the P lan ^tary 

Q. How far are they distant? 

A. The nearest fixed star is supposed to be diVnnt 
from the Earth 2,940,000,000 miles. 

Q. What is to be observed of their light and motion ? 

A. lne fixed stars are supposed to be stationary 
bodies, and shining by their own light. 

Q. How are they classed ? 

A. They have been classed into six magnitudes, 



ASTRONOMY. 47 

namely ; the largest are called stars of the first 
magnitude ; the next stars, of the second ; and so 
on to the sixth, which are the least. 

Q. How is a star distinguished from a planet ? 

A. The fixed stars twinkle, or have an unsteady 
light ; whereas, the planets shine with a steady light. 

Q. Is there any other distinction ? 

A. The fixed stars keep the same relative distance 
from each other ; while the planets are seen in various 
parts of the heaven. 

Q. Is there any other method of distinguishing the 
planets from the fixed stars ? 

A. The planets are sometimes seen with the naked 
eye during the day, and are always visible before 
the fixed stars in the evening. 

Q. What are telescopic stars ? 

A. The telescopic stars are such as cannot be seen 
without the aid of the telescope. 

Q. What are the uninformed stars ? 

A. The uninformed stars are such as are not ar- 
ranged under any particular constellation. 

Q. How many stars are supposed to be visible at 
any one time ? 

A. Not more than 1000 stars are above the horizon, 
visible to the naked eye at one time. 

Q. What are periodical stars? 

A, Periodical stars are such as appear and disap- 
pear : thus, some stars known to the ancients, are 
now invisible ; and many which are visible, were not 
noticed by the ancients. 

Q. What is the supposed cause ? 

A. A periodical star is supposed to turn slowly on 
its axis, and to have one dark side, and when that 
is turned toward us, the star is invisible. 

Q. How is the situation of the fixed stars known ? 

A. To know the situation of the stars, they are 
divided into constellations. 



48 



CATECHISM OF 



CHAPTER XXIV. 

Constellations. 

Q. What is a Constellation ? 

A. A Constellation is an imaginary figure formed 
by a group of contiguous stars. 

Q. How many stars are there in the nothern hemi- 
sphere ? 

A. There are 1251 stars in the nothern hemisphere 

y. Mow many of each magnitude ? 
^'I\ the no ?' th ? rn hemisphere there are 6 stars of 
onn fi ™* ma §Mtude, 24 of the second, 96 of the third, 
200 of the fourth, 291 of the fifth, and 635 of the 
sixth magnitude. 

Q. How many stars are there in the zodiac ? 

A. lnere are in the zodiac 1014 stars. 

Q. How many of each magnitude ? 

A. In the zodiac are 5 stars of the first magnitude, 

18W IF S *£l nd ' ^.°L the third ' 120 of the fourth 
183 of the fifth, and 646 of the sixth magnitude. 

<£ How many stars are there in the southern hemi- 
spnere ( 

A. In the southern hemisphere there are 863 stars. 
H. Mow many of each magnitude ? 
rf'^ Th f e ; are in . the southern hemisphere, 9 stars 

?wS e ioS ** m *^ tude ' 3 i? f the second > 84of ^e 
third, 190 of the fourth, 221 of the fifth, and 324 of 
the sixth magnitude. 
<?. In the northern hemisphere, zodiac, and southern 

nkud?? many StarS are there of each ma S" 

cif* In . ^th hemispheres and zodiac there are 20 
stars of the first magnitude, 76 of the second, 223 

IfifU ^ ' -?u° f the . four ^ 6 ^ of the fifth and 
10U4 ot the sixth magnitude. 



ASTRONOMY. 49 

Q. How many constellations are there ? 

A. There 91 constellations, viz.: 34 in the northern 
hemisphere, 12 in the zodiac, and 45 in the southern 
hemisphere. 



CHAPTER XXV. 

Constellations north of the Zodiac. 

DIVIDED INTO LESSONS. 

Lesson I. 

Names of Constellations. No. of Remarkable Stars. 

STARS. MAGNITUDES. 

1 Ursa Minor The Little Bear 24 Pole Star 2 

2 Ursa Major The Great Bear.. ..87 Dubbe 1 

« f Perseus Perseus 59 Algenib 2 

{ Caput Medusae...Medusa , s Head Algol 2 

4 Auriga ..The Wagoner 56 Capella 1 

5 Bootes 54 Arcturus 1 

Lesson II. 

6 Draco The Dragon 60 Rastaben.. 3 

7 Cepheus 35 Aldermin 3 

8 f Canes Venatici, or The Hounds 25 

{ Asterion and Chara. 

9 Cor Caroli Charles' Heart ...3 

10 Triangulum The Triangle 11 

Lesson III. 

11 { isss^^ } The Liuie Trian ^- 5 



50 CATECHISM OF 

12 Musca The Bee or Fly 6 

13 Lynx 44 

14 Leo minor The Little Lion. ...24 

15 Coma Berenices...Berenice , s Hair 40 

16 Cameleopardalus..The Cameleopard..58 

Lesson IV. 

17 Mons Maenalus.... Mount Maenalus.,.. 11 

18 Corona Boreas {^^^m ^ 

19 Serpens The Serpent 50 

20 Scutum Sobieski..Sobieskrs Shield.... 8 

{Hercules cum f Hercules with the 
Ramo et Cer- < Branch and Cer- 
bero.... (berus 113 Ras Algiatha., 

Lesson V. 



20 f Serpentarius J The Serpent Hol- 

{ sive Ophiucus. \ der 67 Ras Alhagus....3 

23 ( Si P ° ni - 1 Poniatowski's Bull. 7 



{atowski. 



24 Lyra The Harp 22 Vega 1 

nr f Vulpecula et f The Fox and 

** \ Anser....... 1 Goose 37 

26 Sagitta The Arrow 18 

Lesson VI. 

»{K1± :}?^ *° 

28 Delphinus The Dolphin 18 

29 Cygnus The Swan 73 Deneb Adigel...l 

30 Equulus The Colt 10 



ASTRONOMY. 51 

31 Lacerta The Lizard 16 

32 Pegasus The Flying Horse.. 85 Markab 2 

33 Andromeda 66 Almaac 2 

. n f The Lady in the 

34 Cassiopeia j Cfaair J 55 gchedar g 



CHAPTER XXVI. 

Constellations in the Zodiac. 

NORTHERN CONSTELLATIONS. 

Lesson VII. 
In Spring. 

1 Aries The Ram 66 

2 Taurus The^Bull 140 Aldebaran 1 

3 Gemini The Twins 85 Castor & Pollux. 

Summer. 

4 Cancer The Crab 83 Acubens 1 

5 Leo The Lion 95 Regulus 3 

6 Virgo .The Virgin 110 Spica Virginis..l 

SOUTHERN CONSTELLATIONS. 

Lesson VIII. 
Autumn. 

7 Libra The Scales 51 Zuhenich Mali.2 

8 Scorpio The Scorpion 44 Antares 1 

9 Sagittarius ...The Archer 69 



52 CATECHISM OF 



Winter. 

10 Capricornus The Goat 51 

11 Aquarius The Water-bearer.108 

12 Pisces The Fishes 112 



CONSTELLATIONS SOUTH OF THE ZODIAC. 

Lesson IX. 

1 Phoenix The Phoenix 13 

f Officina Sculp- 

J |toria 12 

3 Eridanus The River 77 Achernar ....1 

4 Hydrus The Water Snake..l0 

5 Cetus The Whale 80 Menkar 2 

« f Fornax j The Chemical Fur- 

\ Chemica J nace 14 

Lesson X. 

7 Horologium The Clock 12 

s f Reticulus 

I Rhomboidalis 10 

9 Ziphias The Sword Fish.... 7 

10 Cela Praxitellis...The Gravers 16 

11 Lepus The Hare 19 

Lesson XI. 

12 Columba Noachi..Noah , s Dove 10 

13 Orion .13 Betelguese 

14 Argo Navis The Ship Argo 50 Canopus. 

15 Canis Major The Great Dog 30 Lirius. 



ASTRONOMY. 53 

16 { p^fX! } The P^r's Easel.8 

17 Monoceros The Unicorn 31 

Lesson XII. 

18 Canis Minor The Little Dog 14 Procyon 1 

19 Chamaeleon The Chameleon 10 

oa -n • XT x- f The Mariner's 

20 PyxislNautica..| Compass 4 

21 Pisces Volans The Flying Fish... 8 

22 Hydra The Hydra 60 Cor Hydra. 

23 Sextans The Sextant... 4 

Lesson XIII. 

24 Robur Carolinum.The Royal Oak 12 

«t f Machina 
{ Pneumatica. 

26 Crater The Cup 11 Alkes 3 

27 Corvus The Crow 9 Algorab 3 

28 Crux The Cross 6 

29 Musca The Indian Ely.... 4 

Lesson XIV. 

BOApisIndica {^^.<^ n 

31 Circinus The Compass 4 

32 Centaurus The Centaur 36 

33 Lupus The Wolf 24 

34 Qurdra Euclids.... Euclid's Quadrant.12 

Lesson XY. 

35 f Triangular j The South Tri- 

{ Australe J angle 5 

5* 



j The Air Pump 3 



54 



CATECHISM OF 



35 Ara The Altar 6 

37 Telescopium The Telescope 9 

38 f Corona Aus- ) The Southern 

( tralis J Crown 12 

39 Pavo The Peacock 14 

Lesson XVI. 

40 Indus The Indian 12 

41 Microscopium The Microscope 10 

42 f Octans Had- j Hadley's Quad- 

- ( leianus J rants 43 

43 Grus The. Crane 14 

44 Toucan The Amer Goose... 9 

45 Piscis Australis... The Southern Fish.29 



CHAPTER XXVII. 



Tlie Aurora Borealis; Zodiacal Lights; The Galaxy, 
or Milky Way. 

Q. What is meant by the Aurora Borealis? 

A By the aurora borealis, we mean those streaks 
of light, which in the polar regions, during the frost 
of winter are frequently seen in the sky. 

Q. Can any reason be assigned for such appear- 
ances ? r 

A. The aurora borealis has a resemblance to light- 
ning, and its origin has been ascribed to electricity. 

Q. Where is the aurora borealis seen with greater 
brilliancy ? 

A. It is seen with greater brilliancy in the northern 



ASTRONOMY. « 55 

latitudes, where its brightness exceeds the light of 
the Moon. 

Q. Of what use is this light? 

A. In the high northern latitudes, the aurora bore- 
alis supplies in a great measure the absence of the 
Sun. 

Q. What is meant by zodiacal light ? 

A. The zodiacal light is a beam of light of a tri- 
angular form, seen before sunrise and after sunset, 
with the base toward the Sun. 

Q. When is this light clearest ? 

A. About the beginning of March, in the evening, 
and in September, in the morning, the zodiacal light 
is clearest. 

Q. What is the supposed cause ? 

A. The general opinion is, that the light proceeds 
from the Sun's atmosphere. 

Q. What is the Milky Way ? ^ 

A. The milky way is a whitish zone, nearly en- 
circling the heavens. 

Q. What is the cause ? 

A. Dr. Herschel, upon examining the milky way 
with a very powerful telescope, concludes, that the 
luminous appearance proceeds from the vast number 
of stars which it contains. 

Q. How many stars have been observed ? 

A. In a part of the milky way, 15 degrees in length, 
and two in breadth, Dr. Herschel distinctly enume- 
rated 50,000 stars. 



56 CATECHISM OP 

CHAPTER XXVIII. 

The Tides. 

Q. "What is meant by the tides ? 

A. The tides are two periodical motions of the 
waters of the ocean, called flux and reflux. 

Q. How does the sea flow ? 

A. The water of the sea flows from south toward 
north, and entering the mouths of rivers, it drives 
back the water, and stops their current. 

Q. How long does the influx continue ? 

A. The tides flow for the space of 6 hours, and 
seem to rest for 15 minutes, which time is called 
high water. 

Q. What then takes place ? 

A. The ebb or reflux then begins, and continues 
for six hours, when the rivers resume their natural 
course. 

Q. At the end of the reflux, what happens ? 

A. The waters rest for 15 minutes, which is called 
low-water, when the sea again begins to flow ; thus 
the flux and reflux continue alternately. 

Q. How many times does the tide ebb and flow 
every day ? 

A. The tide ebbs and flows twice every 24 hours. 

Q. Does high-water always happen at the same 
time, in every place ? 

A. The time of high-water is every day 48 minutes 
later than on the preceding day. 

Q. Why does this happen ? 

A. The tides happen later 48 minutes every 24 
hours, because the Moon is 24 hours 48 minutes 
from leaving a meridian till she arrives at the same 
again ; or because a lunar day is 48 minutes longer 
than ours. 



ASTRONOMY. 57 

CHAPTER XXIX. 

Theorij of the Tides. 

Q. What is the cause of this motion of the waters? 

A. The flux and reflux are occasioned by the at- 
traction of the Moon and the Sun, but more especially 
of the former. 

Q. How does attraction produce this flux and re- 
flux? 

A. The attraction of the Moon acting upon the 
water, which on account of its fluidity is more easily 
moved than the solid parts of the Earth, the water 
becomes elevated when that attraction exists. 

Q. Where is the Moon when it is high-water at any 
place ? 

A. The Moon is on or near the meridian of the 
place, when it is high-water at that place, or else she 
is on or near the opposite meridian. 

Q. When are the tides highest ? 

A. The tides are greatest at the new and full Moon. 

Q. Why are they highest at those times? 

A. The tides are highest at changes, because the 
Sun and Moon are in conjunction, and conspire to 
raise the waters, and occasion spring tides. See 
Plate II. Fig. g. 

Q. When are the lowest tides ? 

A. The lowest tides happen when the Moon is in 
her first and last quarters. See Plate II. Fig. f. 

Q. What is the cause ? 

A. When the Moon is in her quadratures, she is in 
opposition to the Sun ; and the attraction of the one 
acts against that of the other ; thus the Moon not 
only loses the assistance of the Sun to raise the 
waters, but finds him acting quite the contrary. 



58 CATECHISM OF 

Q. At what season are the tides highest ? 

A. The tides are highest at the vernal and autum- 
nal equinoxes. 

Q. Why are they highest at those seasons ? 

A. The highest spring tides happen at the equi- 
noxes, because the Sun is nearer the Earth in Sum- 
mer than in Winter. 

Q. How is it that it is high-water at the meridian 
directly opposite to the Moon ? 

A. It is high-water to us when it is at the opposite 
meridian, or 180 degrees distant, because the Earth 
turns on her axis, and the water rises by centrifugal 
force. 

Q. By what force is it raised under the Moon ? 

A. The water rises as the Moon passes, by the 
Moon's centripetal force, or by the joint centripetal 
force of the Sun and Moon. 



CHAPTER XXX. 

Atmosphere; Wind; Rain, doc. 

Q. What is the atmosphere ? 

A. The Earth's atmosphere is the air which sur- 
rounds the Earth to the height of 45 miles, and is 
the support of animal and vegetable life. 

Q. Of what does it consist ? 

A. The atmosphere consists of nitrogen, oxygen, 
and carbonic acid gas. 

Q. What is the weight of the atmosphere ? 

A. The weight of the atmosphere upon every square 
foot on the Earth's surface is 2160 pounds ; but it 
becomes gradually thinner, so that at the tops of 
very high mountains it is difficult to breathe. 



ASTRONOMY. 59 

Q. Wbat is Wind? 

A. A current of air put In motion. 

Q. What is the cause of its motion 

A. When air is rarificd by the heat of the Sun it 
becomes light, and rises, then the heavier air rushes 
in to supply its place, and produces wind. 

Q. Why then does the wind change its direction ? 

A. It is owing to the change of the Earth's position 
with regard to the Sun ; also to the influence of 
mountains, valleys, oceans, &c. 

Q. How are the winds divided ? 

A. In Trade-winds, and Variable winds. 

Q. Of how many kinds are the trade-winds? 
•A. They are of two kinds, the shifting trade-winds 
and the trade-winds. 

Q. What are the shifting trade-winds ? 

A. The shifting trade-winds are those which blow 
one-half the year from the southwest and the other 
half from the northeast. 

Q. Where do they prevail ? 

A. In the Indian Ocean. 

T. Describe the Trade-winds. 

P. They are those winds which always blow in the 
same direction ; on the north of the equator from 
the east and northeast, on the south side from the 
east and southeast. 

Q. Where do they prevail ? 

A. In the Atlantic and Pacific Oceans, between the 
equator and 25 degrees of north and south latitude. 
- Q. What are Variable winds ? 

A. Those which are continually changing from 
day to day, owing to the inequality of the Earth's 
surface. 

Q. Where do they prevail ? 

A. Beyond the 40th degree of latitude. 

Q. What are Land and Sea Breezes? 

A. Those which blow a certain number of hours 



60 CATECHISM OF 

from the land, and then a certain number of hours 
from the sea. They prevail in the torrid zone. 

Q. What are Yapors ? 

A, They are formed by watery particles, separated 
from the land or water by the action of the Sun ; 
being lighter than the air, they rise and float in it. 

Q. What are clouds ? 

A. They consist of vapors exhaled from the sea 
or land : when these vapors rise to a height where 
their density is equal to the surrounding air, they 
unite and become heavier. 

Q. What is Rain ? 

A. When clouds become so condensed and heavy 
that the air cannot support them, they descend in- 
the form of rain. 

Q. Where does the most rain fall during the year? 

A. At the equator ; because the heat of the Sun 
being there the greatest, produces the greatest ex- 
halations. 

Q. What is Snow? 

A. Snow is composed of vapors frozen while small, 
which being but little heavier than the air, descend 
with gentle motion to the earth. 

Q. What is Hail? 

A. It is composed of vapors condensed into drops, 
which by some sudden change in the atmosphere are 
frozen while falling. 

Q. What are Fogs and Mists ? 

A. They are thin clouds resting on the surface of 
the earth. 

Q. What is the Twilight ? 

A. The morning and evening twilight is the re- 
flected light of the Sun through the medium of the 
atmosphere, when he is within 18 degrees of the 
horizon. 



ASTRONOMY. 61 

CHAPTER XXXI. 

Of Globes, 

Q, What is a Globe ? 

A. It is a round body. 

Q. How many kinds of globes are there ? 

A. Two — Terrestrial and Celestial. 

Q. What does the terrestrial globe represent ? 

A. The figure of the Earth, with its oceans, con- 
tinents, rivers, kingdoms, &c, delineated on its sur- 
face. 

Q. What is represented on the celestial globe ? 

A. On its surface are delineated all the appearances 
of the heavens. 

Q. In viewing the representations on these globes, 
where is the eye supposed to be placed ? 

A. On the surface of the terrestrial globe, and at 
the centre of the celestial. 



62 



CATECHISM OF 



PROBLEMS 

PERFORMED BY THE 



TERRESTRIAL GLOBE. 



PROBLEM I. 

To find the latitude of any given place. 

Rule. — Bring the place to the graduated side of 
the brazen meridian, and the degree of the meridian 
over the place is the latitude. 

Q. What is the latitude of London ? 

A. Fifty-one and a half degrees north. 

Q. What is the latitude of St. Helena ? 

A. About sixteen degrees south. 

Q. What places have no latitude ? 

A. The directly under the equator. 

Q. Find all the places which have no latitude. 

A. All places between the equator and south pole 

are in south latitude, and those between the equator 

and north pole are in north latitude. 

Find the latitude of the following places : 
Amsterdam, Cape of G. H. Halifax, 

Aleppo, Cape Horn, Ispahan, 

Athens, Cario, Lima, 

Algiers, Dantzic, Lisbon, 

Bengal, Dublin, Madrid, 

Boston, Edinburg, Madras, 

Batavia, Fez, Moscow, 



ASTRONOMY. 



63 



New York, 
Norfolk, 
Paris, 
Philadelphia, 



Prague, 
Quito, 
Rome, 
Stockholm, 



Teneriffe, 
Tripoli. 
Washington, 
Vienna. 



PROBLEM IT. 

To find the longitude of any given place. 

Rule. — Bring the place to the brazen meridian, 
and the degree of the equator under the meridian, is 
the longitude. 

Q. What is the longitude of Washington ? 

A. About seventy-seven degrees west. 

Q. What is the longitude of Madras ? 

A. Eighty degrees east. 

Q. What is the greatest longitude a place can 
have? 

A. One hundred and eighty degrees. 

Q. How do you find all those places which have the 
greatest longitude ? 

A. Bring the one hundred and eightieth degree of 
the equator to the meridian, and all the places under 
the meridian have the greatest longitude. 
Find the longitude of the following places : 

Knoxville, 

London, 

Leghorn, 

Jerusalem, 

Montreal, 

New Orleans, 

Nankin, 

Oporto, 

Pekin, 



Alexandria, 


Calcutta, 


Archangel, 


Cadiz, 


Aleppo, 


Delhi, 


Albany, 


Dresden, 


Baltimore, 


Damascus, 


Berlin, 


Gibraltar, 


Constantinople, 


Havana, 


Charleston, 


Hamburg, 


Canton, 


Buenos Ayres, 



64 

Petersburg, 

Portsmouth, 

Quebec, 

Rhodes, 

Syracuse, 



CATECHISM OF 

Hio Janeiro, 
Caraccas, 
Sierra Leone, 
Tunis, 
Tyre, 



Toulouse, 

Venice, 

Vesuvius, 

Warsaw, 

Washington. 



PROBLEM*TII. 

The hour of the day at any place being given, to find 
what o clock it is at any other place. 

+.?i! 7L ^~~~ Bring the Place, where the hour is given 
to the brazen meridian ; set the index to the given 
™ 5 ? ^ ^ / obeti11 the proposed %7e 
C^£t mendian; thei ^^PomUhe e 

^^'"h 11 the P lace squired be east of the given place 
ward g G Westward '* if t0 &e west, turn the|lobe east- 

JL^ll 11 l fc . is twe l v , e °' clock at noon in London, 
what is the time at Mauritius and Philadelphia ? 

PMa F d°el^ at MaUriti ^ and ™> AM > ^ 

^ W } en *\H eight , ° ,cIock A « M - at Boston, what 
is the time at Acapulco and Cape Farewell? 

Farewell M *' at Acapulco ' and ten, A. M., at Cape 

isit aT hen h iS midni S ht at New York, what o'clock 

T& Canton, New Orleans, 

Rome Calcutta, Rio Janeiro, 

Petersburg, Cairo, Ascension Islands ? 



ASTRONOMY. 



65 



Q. When it is noon at Lisbon, what is the hour at 
Quebec, Cape Horn, Babelmandel, 

Jerusalem, Bermudas, Botany Bay, 

St. Helena, Cape Comorin, Athens, 

Mexico, Pekin, Tripoli ? 



PROBLEM IV. 



To find the distance in miles between any two places 
on the Globe. 

Rule. — Lay the quadrant of altitude over both 
places, and it will show the number of degrees, 
which multiply by sixty-nine and a half, and it will 
give the distance in miles. 

Q. What is the distance between London and 
Jamaica ? 

A. Sixty-seven and a half degrees, or four thousand 
six hundred and ninety-one miles. 

Q. What is the distance between New York and 
Paris ? 

Q. What is the distance between Baltimore and 
London ? 
Q. What is the distance between 
Cadiz and Petersburg, 
Washington and Madrid, 
Cape Horn and Good Hope, 
Philadelphia and Venice, 
New York and London, 
• Cuba and Cyprus, 
Charleston and Fez, 
London and Bombay ? 

6* 



66 CATECHISM OF 



PROBLEM V. 

The day of the month being given, to find the Sun's 
place or longitude in the ecliptic and its declination. 

Rule.— Look for the given day in the circle of 
months on the horizon, and opposite to it in the circle 
of signs, are the sign and degree the sun is in on 
that day. Find the same sign and degree in the 
ecliptic, and it will be the Sun's place or longitude ; 
bring this place to the meridian, and you will have 
the declination. 

Q. What is the Sun's longitude and declination on 
the twenty- second of February ? 
A. Its longitude is three hundred and thirty-seven 
and a half degrees, or four and a half degrees in 
Pisces ; its declination is ten degrees south. 

Q. What is the Sun's longitude and declination on 
the fifteenth of April ? 

A. Its longitude is twenty-five and a half degrees 
in Aries ; its declination is ten degrees north. 

Q. What is the Sun's declination on the twenty- 
first of June ? 

Q. What is the Sun's place and declination on the 
twenty-second of December ? 

Q. What is the Sun's place in the ecliptic, and its 
declination, on each of the following days ? 

March 30th, September 16th, 

April 4th, October 5 th, 

May 12th, November 2d, 

June 9th, December 29th, • 

July 13th, January 7th, 

August 8th, February 16th, 



ASTRONOMY. 67 



PROBLEM VI. 



To rectify the globe for the Latitude, Zenith, and Sun's 
place on any day. 

1. For the Latitude. Elevate the pole till the 
horizon cuts the brass meridian in the degree corres- 
ponding to the latitude of the place. 

2. The place given is then in the Zenith. 

3. Then (by Problem V,) find the Sun's place for 
the given day, bring it to the meridian, and set the 
index to twelve. 

Note.— If the place be in north latitude, elevate the north 
pole, if in south latitude, elevate the south pole. 

1. Rectify the globe for the latitude of London on 
the tenth of May. 

In this case elevate the north pole fifty-one and a 
half degrees, then London will be in the zenith; over 
it screw the quadrant of altitude ; the tenth of May 
on the horizon answers to the twentieth degree of 
Taurus, which find on the ecliptic, and bring it to 
the meridian, and set the index to twelve. This is 
the position of the globe as it appears to the inhabi- 
tants on the tenth of May. 

2. Rectify the globe for 

Xew York, 12th January, 
Boston. 6th February, 

Constantinople, 9th March, 

Petersburg, 10th April, 

Madrid, 16th September, 

Cape Horn, 15th November, 

St. Jago, (Chili) 14th December, 

Gallipagos, 19th October. 



CATECHISM OF 



PROBLEM VII. 



To find at ivJiat hour the Sun rises and sets at any 
place, any day in the year, and the length of the 
day and night at that place. 

Rule.— 1. Rectify the globe (by Problem VI,) for 
the latitude of the place ; find the Sun's place in the 
ecliptic (by Problem V,) and bring it to the meridian, 
and set the index to twelve ; bring the Sun's place 
to the eastern edge of the horizon, and the index 
will show the hour of rising; bring it to the western 
edge of the horizon, and the index will show the 
hour of setting. 

2. Double the time of sun rising, and it will give 
the length of the night ; double the hour of sun set- 
ting, and it will give the length of the day. 

Q. What time does the sun rise and set at New 
York on the tenth of May, and what is the length of 
the day and night ? 

A. It rises fifty-six minutes past four ; sets four 
minutes past seven ; length of the night nine hours 
fifty-two minutes ; of the day fourteen hours eight 
minutes. 

Q. What is the time of sun rising and sun setting, 
and the length of the day and night, at each of the 
following places on the day mentioned ? 
Washington city, 4th of May, 
Constantinople, 14th of June, 
London, 15th of July, 

Rio Janeiro, 8th of September, 

Cape Horn 1st of December, 

• Rome> 5th of January, 

Naples, 9th of October, 

Canton, 8th of August, 

Boston, 7th of November ? 






ASTRONOMY. 69 



FROBLEM VIII. 

Tlie month and day of the month being given, to find 
those places where the Sun does not set, and where 
it does not rise on the given day. 

Rule. — Find the Sun's declination (by Problem V,) 
elevate the pole for the declination in the same man- 
ner as for the latitude ; turn the globe on its axis, 
and on the places round the pole above the horizon 
the Sun does not set ; and on the places round the 
other pole below the horizon the Sun does not rise, 
on that day. 

Q. How much of the south frigid zone is darkened, 
and how much of the north frigid zone is enlightened, 
on the twentieth of May ? 
A. Twenty degrees round each pole. 
Q. On which pole does the Sun rise on November 
the sixth ? 

Q. Which frigid zone, and how much of it, has 
constant day on August 4th ? 

Q. How much of the south frigid zone has constant 
day on the following days : 

October 1st, January 9th, 

October 20th, February 10th, 

November 19th, February 20th, 

December 22d, March ,.• 1st? 

Q. What days in the year does the Sun shine equal- 
ly on both poles ? 



CATECHISM OF 



CELESTIAL GLOBE. 



PROBLEM I. 

To find the right ascension of the Sun or a star. 

Rule. — Bring the Sun's place in the ecliptic or 
the star, to the brass meridian, then the degrees of 
the equinoctial under the meridian, reckoning from 
Aries eastward, is the right ascension. 

Note. — The Sun's place in the ecliptic is found by Problem 
V, Terrestrial Globe. 

Q. What is the Sun's right ascension on the 19th 
of April ? 
A. Twenty-seven and a half degrees. 
Q. What is the Sun's right ascension on the 1st 
December ? 

A. Two hundred and forty-seven degrees fifty 
minutes. 
Q. What is the Sun's right ascension on — 
November 6th, May 7th, 

March 4th, August 10th, 

April 20th, September 14th, 

June 16th, October 23d, 

July 29th, December 10th? 

Q. What is the right ascension of Aldebaran ? 
A. Sixty-six degrees six minutes. 
Q. What is the right ascension of — 

Alioth, Castor, Menkar, 

Arcturus, Algol, Pleiades, 

Achernar, Fomalhaut, Procyon, 

Bellatrix, Hyades, Regulus, 



ASTRONOMY. 71 

Rastaben, Sirius, Pollux, 

Rigel, Antares, Acubens ? 

Note. — The preceding stars, and their planes in the con- 
stellations, may all be found in the preceding table. 



PROBLEM II. 



To find the declination of the Sun or a star. 

Rule. — Bring the Sun's place in the ecliptic or 
the star, to the brass meridian, and the degree of 
the meridian over that place will be the declination. 

Q. What is the declination of the Sun, April 19th ? 

A. Eleven degrees nineteen minutes north. 

Q. What is the Sun's declination, 

January 18th, April 12th, 

February 12th, May 23d, 

March 2d, June 21st? 

Q. What is the declination of Aldebaran ? 

A. Sixteen degrees six minutes. 

Q. What is the declination of — 

Atair, Arcturus, Regulua 

Algenib, Procyon, Rigel ? 



72 CATECHISM OF 



PROBLEM III. 



The latitude of the place, the day and hour being 
given, to place the globe so as to represent the ap- 
pearance of the heavens at that time at the place; 
and to point out the situations of the several stars. 

Rule. — Elevate the pole for the latitude of the 
place ; find the Sun's place in the ecliptic, and bring 
it to the meridian, and set the index to 12 ; if the 
time be afternoon turn the globe westward, if in the 
forenoon, turn it eastward, till the index points to 
the given Hour. The surface of the globe then re- 
presents the appearance of the heavens at that place. 

Q. Represent the appearance of the heavens for 
January 13th, 4 o'clock, A. M., and 8 o'clock P. M. 



PROBLEM IV. 

To find the latitude or longitude of a given star. 

Rule.— Screw the quadrant on the pole of the 
ecliptic, bring the star to the meridian, and the de- 
grees of the quadrant between the ecliptic and star, 
show the latitude, and the degree of the ecliptic 
under the graduated edge of the quadrant is the 
longitude. 

Q. What is the latitude and longitude of Arcturus? 

A. Latitude thirty- one degrees north, longitude 
two hundred and one degrees. 

Q. What are the latitudes and longitudes of — 
Fomalhaut, Canis Major, 

Canis Minor, Regulus ? 



ASTRONOMY. 73 



PROBLEM V. 

The latitude and longitude of a heavenly body being 
given, to find its place on the globe. 

Rule. — Fix the quadrant as in the last problem, 
and place it on the given degree of longitude in the 
ecliptic ; then seek the given latitude on the quad- 
rant, and under that degree is the place sought. 
« 
Q. What is the star whose longitude is two hun- 
dred and one degrees, and its latitude thirty-one de- 
grees north ? 
A. Arcturus in Bootes. 

Q. What stars have the following longitudes and 
latitudes ? 

Longitudes. Latitudes. 

66J degrees, 5| degrees south, 

299 degrees, 29 degrees north, 

85 degrees, 16 degrees south. 



PROBLEM VI. 



The right ascension and declination of a heavenly body 
being given, to find its place on the globe. 

Rule. — Bring the given right ascension to the 
brass meridian, and under the given degree of de- 
clination on the meridian, is the place required. 

Q. What is the star, whose declination is thirty 
degrees forty minutes south, and right ascension 
three hundred and forty-one degrees thirty-eight 
minutes ? 

A. Fomalhaut in the Southern Fish. 
7 



74 ASTRONOMICAL TERMS. 

Q. What are the stars whose right ascension and 
declinations are as follows : 

Right ascension. Declination. 

183° 44' 69° 59' south, 

277° 32' 38° 39' north. 



APPENDIX, 

CONTAINING 

ASTEONOMICAL TERMS. 



Aberration, is an apparent change of place in the 
fixed stars, arising from the motion of the Earth 
combined with the motion of light. 

Achronical, rising or setting of a planet or star, 
is, when it rises at sunset, or sets at sunrise. 

Altitude, is the height of the Sun, Moon, or stars, 
above the horizon. 

Amplitude, is an arc of the horizon, contained be- 
tween the true east or west point of the heavens, 
and the centre of the Sun or star, at its rising or 
setting. 

True Anomaly, is the distance of a planet in signs, 
degrees, &c, from that point of its orbit which is the 
farthest from the Sun. 

Antceci, is a name given to those inhabitants of 
the Earth, who live under the same meridian, and 
at equal distances from the equator, but opposite 
sides of it. 

Antecedentia, is a motion of any of the heavenly 



ASTRONOMICAL TERMS. 75 

bodies, which is contrary to the order of the signs: 
as, from Aries toward Pisces, &c. 

Aphelion, is the place in a planet's orbit when 
farthest from the Sun. 

Apogeon, is that point in a planet's orbit at its 
greatest distance from the Earth. 

Apsides, are two points in a planet's orbit, in 
which it is at its greatest and least distance from the 
Sun ; the line joining those points, is called the line 
of the Apsides. 

Ascensional Difference, is an arc of the equinoctial, 
contained between that point of it which rises with 
the Sun, Moon or star, and that which comes to the 
meridian with them ; or, it is the time the Sun rises 
or sets before or after six o'clock. 

Atmosphere, is that body of air which surrounds 
the Earth. 

Attraction, according to the Newtonian philosophy, 
is that innate principle of matter, by which bodies 
mutually tend toward each other. 

Axis of the Earth, or of a planet, is an imaginary 
line passing through the centre from one pole to the 
other ; or that round which they are supposed to 
perform their diurnal rotations. 

The Azimuth of any celestial object, is an arc of 
the horizon contained between the east or west point 
of the heavens, and a vertical circle passing through 
the centre of that object. 

Cardinal Points, are the east, west, north, and 
south points of the compass. 

Cardinal Points of the ecliptic, are the first points 
of the signs Aries, Cancer, Libra and Capricorn. 

Conjunction, is when two stars seen from the Sun 
or the Earth, appear at the same point of the hea- 
vens, or answer to the same degree of the ecliptic. 
Cosmical rising or setting of a planet or star, is 



76 ASTRONOAnCAL TERMS. 

when it rises with the Sun in the morning, or sets 
with him in the evening. 

Culminating, is a term applied to the Sun, or a 
star when it comes to the meridian of any place. 

Cycle of the Moon, is a revolution of 19 years ; 
in which time the conjunctions and lunar aspects 
are nearly the same as they were 19 years before. 

An Astronomical Bay, the time between two suc- 
cessive transits of the Sun's centre over the same 
meridian ; which always begins and ends at noon. 

Declination of the Sun, Moon, or stars, is their 
distance north or south from the equator, reckoned 
in degrees, minutes, &c, upon a circle which is per- 
pendicular to it. 

Direct, a planet is said to be direct, when it moves 
according to the order of the signs ; as from Aries 
toward Taurus, &c. 

Disc of the Sun or Moon, is its round face; which, 
on account of the great distance of the object, appears 
flat or like a plane surface. 

Digit, in astronomy, is the twelfth part of the 
Sun's diameter, which is often used in the calcula- 
tion of eclipses. 

Eccentricity, is the distance between the centre of 
an ellipsis and either of its foci. 

Elongation, is the angular distance of a planet 
from the Sun, as it appears to a spectator upon the 
Earth. 

Elements, in astronomy, are the requisites necessary 
to determine the theory of a planet, in order to cal- 
culate its position, motion, &c. 

Emersion, is the time when any planet which is 
eclipsed begins to recover its light again. 

Epact, is the Moon's age at the end of the year : 
or the difference between the solar year and the 
lunar one. 

The Equator, is a great circle which separates the 



ASTRONOMICAL TERMS. 77 

northern from the southern hemisphere, consisting 
of twelve stars. 

The Equinoxes, are two points where the ecliptic 
cuts the equator ; so called, because when the Sun 
is in either of these situations, the days and nights 
are equal to each other. 

Erection, is an inequality in the motion of the 
Moon, by which at her quarters, her mean place 
differs from her true one by about 2J degrees more 
than at her conjunction and opposition. 

The Galaxy or milky-way, is a large irregular 
zone, or band of light, which encompasses the 
heavens. 

The Geocentric place of a planet, is that position 
which it has when seen from the Earth. * 

Gibbous, is a term used in reference to the enlight- 
ened parts of the Moon, whilst she is moving from 
the first quarter to the full, and from the full to the 
last quarter, on account of the dark parts appearing 
falcated, or horned, and the light ones convex. 

Golden Numbers, a series of numbers proceeding 
from one to nineteen, which are used in the almanac, 
for determining the times of new and full moons. 

Heliacal rising of a star, is when it emerges from 
the Sun's rays, and appears above the horizon before 
him in the morning. 

Heliacal setting of a star, is when it is so hidden 
in the Sun's beams, as not to be seen above the hori- 
zon after him in the evening. 

Heliocentric place of a planet, is that in which it 
would appear to a spectator placed in the Sun. 

Hespems, a name given to the planet Venus, when 
she appears in the evening. 

Heteroscii, a name given to the inhabitants of the 
temperate zones, because their shadows at noon 
always fall one way. 

The Sensible Horizon, is a circle which separates 
7* 



78 ASTRONOMICAL TERMS. 

planet makes with ^ £ JX <"b.t of one 

up A o? £SK?' jDay ' is <? e odd da 7. whi <* ^ made 
up of the six hours every fourth, or leap-year 

upon the w*. greM oipole .iSgU^SaSi; 

i» Bar, is the same with besseitile • so ealM 
Jr m on e o r ne bemS * ** "*" fa that ^ ^hanTa 

axis in such a manner thaHhe parts of her eastern 
aTternltelr ^ bCC ° me ™ ibIe !^ *Sfi 

from e thi°Z^ e - 0f ,% St f - 0r P lanet ' is ^ distance 
trom the first point of Aries, reckoned in deeree- 
minutes, &c, upon the equator. degrees, 

Lucifer, is the morning star Venus • sn M 1U 
when it is in the east, and^ises before the Sun ' 

Lunar Aspects, are those which the Moon makes 
with any of the other planets • as wh™ !u 
into opposition, trine, quartile, '&T. "*** ^ °° meS 



ASTRONOMICAL TERMS. 79 

The Macula?, are dark spots, appearing on the face 
of the Sun, Moon, and some "of the planets; being 
contradistinguished from faca loz, which are bright or 
shining spots, that, by means of the telescope, are 
sometimes to be seen on the face of the Sun, &c. 

The Magnitudes of the stars are divided into six 
by some, by others into eight sizes, or classes ; of 
which the brightest are called stars of the first mag- 
nitude, about four times less than the Earth. 

The Mean motion of a planet, is that which would 
take place, if it moved in a perfect circle, and equally 
every day. 

A Meridian, is a great circle of the sphere, which 
passes through the zenith and poles. 

A Minute, is the 60th part of an hour in time, or 
of a degree in motion. 

A Lunar, or Periodical Month, is a period of about 
27 days 7 hours and 43 minutes, which is the time 
the Moon is in passing from one point of her orbit, 
to the same point again. 

A Si/nodical Month, is a period of about 29 days 
and a half, which is the time between one conjunc- 
tion of the Sun and Moon and another. 

A Solar or Calendar Month, is the time the Sun 
takes to move through one of the signs of the zodiac, 
which, at a mean, is about 30 days and a half. 

Nebuloe, are clusters of small stars which have 
been discovered by the telescope in different parts of 
the heavens ; and are so called from their cloudy 
appearance. 

A Nocturnal Arc, is that space of the heavens 
which the Sun apparently describes, from the time 
of his setting to the time of his rising. 

Nodes, are two points where the orbit of a planet 
intersects the plane of the ecliptic. 

Nucleus, is a term used by some Astronomers, for 



80 ASTRONOMICAL TERMS. 

the head of a comet ; and by others for the central 
parts of the planets. 

Oblique Ascension, is an arc of the equinoctial, 
contained between the first degree of Aries, and that 
point of it which rises with the centre of the Sun or 
a star. 

Occultation, is when a star or planet is hidden from 
our sight by the interposition of the Moon, or some 
other planet. 

Opposition, is an aspect of the stars or planets, 
when they are 180 degrees distant from each other. 

Orbit of a planet, is the curve or path which it de- 
scribes in its revolutions round the Sun. 

Parallax, is the difference between the places of 
any celestial object, as seen from the surface of the 
Earth and from its centre. 

Parallax of the Earth's annual orbit, is the angle 
at any planet which is subtended by the distance 
between the Sun and Earth ; or, it is that change of 
place in the planets, which arises from their being 
seen from different points of space, as the Earth 
moves round the Sun. 

Penumbra, is a faint shadow, which accompanies 
an eclipse, and occasions a partial obscurity of the 
body to that part of the Earth on which it falls. 

Perioeci, are those inhabitants of the Earth who 
live under the same parallels of latitude, but on op- 
posite sides of the meridian. 

Perigeon, is that point of a planet's orbit in which 
it is at its least distance from the Earth. 

Perihelion, is that point of a planet's orbit in which 
it is at its least distance from the Sun. 

Phases, are the several appearances of the Moon 
and planets, according as a greater or less part of 
their illuminated hemispheres is presented to our 
sight. 

The Primary Planets, are those bodies in our sys- 



ASTRONOMICAL TERMS. 81 

torn, which regard the Sun as the centre of their 
motions. 

Plane, in astronomy, is frequently used for an im- 
aginary surface, which is supposed to cut and pass 
through solid bodies ; and, in this sense, we are to 
understand the plane of a planet's orbit. 

Precession of the equinoxes, a slow motion of the 
two points where the equator intersects the ecliptic, 
which are found to go backwards about 50 seconds 
a year. 

Quadratures, or quarters, are those phases of the 
Moon which take place between the conjunction 
and opposition, and between the opposition and con- 
junction ; one being called the first quarter and the 
other the third. 

Quartile, is an aspect of the planets when they are 
90 degrees, or a quarter of the zodiac distant from 
each other. 

Refraction, is that variation which the rays of light 
suffer in passing through the mediums of different 
densities which occasions the heavenly bodies, when 
viewed obliquely through the atmosphere, to appear 
at a greater height above the horizon than they 
really are. 

Repulsion, is that property in bodies, by which, if 
they are placed just beyond the sphere of each 
other's attraction of cohesion, they mutually fly from 
each other. 

Retrograde, is an apparent motion of the planets 
in some parts of their orbits, when they seem to go 
backwards, or contrary to the order of the signs. 

Revolution, is that motion by which the heavenly 
bodies, in a certain time, return again to the same 
points of their orbits. 

Rotation, is the motion of any heavenly body 
round its axis. 



82 ASTRONOMICAL TERMS. 

The Seasons, are Spring, Summer, Autumn, and 
Winter. 

Sextile, is an aspect of the heavenly bodies when 
they are 60 degrees distant from each other. 

Sidereal Year, is that space of time which the Sun 
takes in moving through the ecliptic, from any fixed 
star to the same star again. 

The Signs, are the twelve constellations of the zo- 
diac: Aries °P, Taurus 8, Gemini II, Cancer g, Leo 
£1, Virgo up, Libra =2=, Scorpio HI, Sagittarius 2, 
Capricornus 14°, Aquarius ^, and Pisces ^. 

Solstitial Points are the two points of the zodiac, 
Cancer and Capricorn ; at which the ecliptic touches 
the tropics, and into which the Sun enters on our 
longest and shortest days. 

Southing of the stars, is the time when they cul- 
minate or come to the meridian. 

Superior Planets, are those those which move at a 
farther distance from the Sun than the Earth ; as 
Mars, Jupiter, Saturn, and Herschel. 

Synodical Month, is the space of time from any 
new Moon to the following one, which is at a mean 
29 days, 12 hours and 45 minutes. 

Syzygies, are those points of the Moon's orbit in 
which she is at the time of her new and full. 

The Telescopic Stars, are those which are only 
discoverable by means of a telescope. 

Transit, is the passing of one celestial body before 
another ; so as to render any part of it invisible. 

Trine, is an aspect of the planets, when they are 
120 degrees distant from each other. 

Twilight, is that faint light which we perceive be- 
fore the rising of the Sun, and after his setting, and 
whichis occasioned by the refraction of the Earth's 
atmosphere. 

Vertical Circles, are the same as azimuth circles, 
or such as are drawn perpendicular to the horizon. 
THE END. 



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